12 days I would limit my time to 2 destinations. I suggest Bangkok and a beach location. I would split time as follows:
Bangkok- 5 days
Beach resort- 5 days
Bangkok 2 days

Your first day or so you will be jet lagged so don't plan on too much activity.

I assume your budget of $200/day is just for hotels, if so that will get you 5 star properties. In Bangkok I suggest staying on the river. The Penninsula (might be somewhat higher in price), Anatara, Sheraton,or ShangriLa.

Other fodors vets will chime in with their thoughts.

I agree with Bill on limiting your destinations to 2 - Bangkok and for a beach location possibly Phuket. In a budget of 200$ per day you can get pretty good hotels in Thailand.

For Bangkok, you can try the Shangri La on the river, a great property. Inside the city a great option is the Four Seasons for their excellent service. If these are running over your limit, Dusit Thani is my personal favorite for good value.

In Phuket, it really depends on the type of resort you like. I'm quite ok with the huge ones like Hilton and Moevenpick but if you are looking for something more cosy, the Banyan Tree gets great reviews.

The Shangri La is a nice hotel but the reason I mention the others is that the others are on the water and include a boat ride to the sky train station. Each of the other hotels have their own boats that take you across the river to the sky train. Its one of the pleasurable experiences in Bangkok - riding the hotel boat each day and enjoying the river traffic and views.

I would spend time in Bangkok, the beach (phuket is easy, Krabi is nicer though) and the north. If you like animals, nature, hiking, I would try to go to Chiang Rai.

I think with 12 days on the ground if you just spent it in Bangkok and Phuket you would not be seeing all that Thailand has to offer. I'd spend 3 nights in Bangkok (2 days) and split my time between other destinations. Flying around Thailand is easy. I disagree with the recommendation to spend 7 days in Bangkok....to each their own.

As for Phuket, I recently stayed in the Banyan Tree. The resort was a bit too big for us with the beach far away, but the grounds were beautiful, with great service. Our villa was amazing, and it was the most basic option. However the place was so spread out that you had to call for a golf cart to ake you to the beach. Personally I prefer Krabi and the Tubkaak - a great boutique resort on a beautiful beach facing Hong Island. Once you get to Bangkok you can easily fly to many places in Thailand.

A lot of people here like staying on the River in Bangkok, which is a more relaxing recommendation. Not sure about the Shangri La, but I stayed in the Royal Orchid Sheraton a few monhs ago and don't recommend it - the rooms are old and not great. For $200 a night in Bangkok, you can do pretty well. Look at the Sukhothai, not on the river, but I've heard good things.

You have a lot of activities on your wish list and with just 12 days you need to determine those activities which are priorities.

Bangkok will meet your requirements for food, culture in bucket loads and has some of the best hotels in the world. As BillT points out, staying on the "wrong" side of the river is not a problem at all and the daily boat trip is a distinct pleasure. Alternatively, the Conrad on Wireless Road is a fantastic hotel and the exec room deals are well worth investigating. We also stayed in the new Aloft hotel last year which is in a great location off Sukumvit and is a really trendy, modern place opposite the Bed Supper Club . It has great rooms at a third of the price of the Peninsula.

Personally, although Phuket has some fantastic, if expensive hotels, I would avoid it at it is way too developed these days. For the beach, Krabi, Khao Lak or some of the smaller beach places will have nicer beaches, smaller hotels and much lower rates. If, as you suggest, you are prepared to drop your budget then have a look at http://www.travelfish.org/country/thailand which will give you a lot of information on some of the less beach places. the andaman coast has some really nice smaller islands that won't be full of Starbucks etc.

To satisfy your requirements for nature , hiking etc. maybe Mae Hong Son in the north of Thailand has some great scenery, minority peoples culture etc. but It really needs around 5 days and this would make beach time difficult in the time available. Click on my screen name to find my recent trip report on this area. Alternatively, a trip to one of the southern National Parks would be great and could be reached from Krabi or Khao Lak 2 or 3 days would be the ideal time for a night or two in a jungle lodge.

BTW congratulations on you forthcoming marriage!

Bangkok - Chiang Mai - Koh Samui - Bangkok , that gives you variety, lots of ideal honeymoon places on Koh Samui with jacuzzi rooms and similar.

If you want beach and nature then Bangkok - Chiang Mai - Khao Lak ( route to Phuket airport and then road north from the airport ) - Bangkok

Thanks so much for all of the replies! I appreciate all of the perspectives and it has helped myself and my fiance to narrow down the kind of trip that we want to have.

At this point I would say that based on the experiences we want to have in Thailand, we want to spend about five or six days in the northern section of the country. It seems that Chiang Mai is popular, and Mae Hong Son sounds like a good option as well. Any suggestions on picking one over the other, or heading to both or another location in the north? Any particularly memorable activities or particular places to see within the northern cities or outside of them? Recommendations for hiking or elephant riding?

We of course want to hit the beaches as well. I would really like to hear opinions regarding Phuket versus Krabi. Are the activities available similar? Will one be more crowded at this time of year vice the other? I imagine both have nice resorts but would anything stand out in Krabi vs Phuket?

Finally, any tips on how quickly after arriving in Bangkok it would make sense to head up north? I'm thinking a night/day in the city and then a flight up north would make the trip the smoothest but this is my first trip to Asia and would love to hear any advice in that regard.

Again, thanks for all the comments.

where will you be coming from? if from north american, the first 3 days can be rough to adust...

doi tung and the opium museum near chiang saen are musts..

some parts of phuket are very undesirable. i personally found ao nang near krabi tooo touristy

As for Phuket vs. Krabi, I think the beaches and views are nicer in Krabi. Agreed with rhkkmk that Ao Nang (the town near Krabi) is much too touristy.

If you're on your honeymoon, I imagine you want to enjoy the resort. Even though Phuket and Krabi both are built up and touristy, I go to them to enjoy the beautiful resorts, beaches, sunsets....Bangkok is a better place to really enjoy Thai culture.

That said, I was at the Tubkaak in Krabi and the beach was just perfect. There are a few resorts on the strip of beach where the Tubkaak is located (Tubkaak beach), they all looked nice and are in different price ranges. The beach faces Hong Island, and has the most amazing sunsets I've seen. I'd avoid the Sheraton in Krabi, it's too big and impersonal. Same for the Sofitel, which has a big road running between the hotel and the beach. In Krabi there are some nice day trips you can do, one up 1300 steps to a temple with amazing views, hot springs. We went to the Crystal Lagoon, and were the only western tourists there, which was nice.

As for Phuket, I didn't leave the Banyan Tree. The beach was nice, but the water was not as clear as in Krabi (but this might just be due to this particular beach) and the views weren't great.

we like the sheraton krabi a lot, but it is big and less personal than say the amari vogue, up the road which is fab, imo... the sheraton has the advantage of a couple of decent restaurants just across the street, esp the thai one.

i still prefer the jw marriott in khao lak above all the others..

Phuket is rather crowded, if you want the nightlife fun then Phuket is the best, but if you want some private time, you should rather opt for Phi Phi Island. You will have a great adventurous honeymoon in Thailand

Rhkkmk, when was the last time you went to the JW in Khao Lak?I am asking because I recently considered buying a trip there because they had some REALLY reasonable deals ($300 US for 3 nights including breakfast, wifi,etc). However, the hotel resorting to groupon makes me a bit skeptical and makes me wonder if the place has gone downhill...

The Amari is next to the Tubkaak that I recommended - that section of the beach is just beautiful. The Amari is bigger than the Tubkaak with a bigger pool. From a distance the decor looked a bit more Thai (Tubkaak is a bit more...Asian/contemporary). Both are great honeymoon choices.

i was last at the jw in nov of 2011.... i will be there again in oct.

its a big place and tourism is down, so i am not surprised they use groupons to help fill the place up. offering groupons does not mean a place is in trouble, imo.

I appreciate all of the replies!

A couple of more questions: Any way to compare Phuket and Ko Samui as destinations? I am finding good lodging deals in Ko Samui and what I've read about leads me to believe that you can stay fairly active while staying there (fishing, diving, hiking). Are they both equally crowded?

Any suggestions for the beach area with the most outdoor activities available? It seems like snorkeling and diving are fairly common while it is more difficult to find any kind of hiking near the beach.

Any particular tour companies or areas in Chiang Mai to hike that have great mountain scenery? It seems like there are so many choices.

Thanks again for all of the thoughts.

i think you will find samui less crowded..

samui however is more expensive to fly to, but its worth it..

Samui only has one good beach, Chaweng beach, with fine white sands and it can get crowded. The other beaches on the island are either sand with rocky bottoms or have slushy bottoms. Samui, however, is more laid back and cheaper as a whole than Phuket and the surrounding area.

Phuket, IMO, is better than Samui but at a much higher price. Beaches on Phuket is nicer and if you consider fishing then the seas around Phuket is far superior to Samui.