A friend and I are traveling to Asia this summer and are trying to figure out whether to go to Cambodia or Laos. We are flying into Hong Kong and meeting a group in Vietnam and are trying to decide what to do in between. We should have about a week to do either Cambodia or Laos.

Any suggestions?

Also, when it comes to getting a Vietnam Visa, is it best to do it beforehand or is it possible to do it at one of the border crossings? Same for Cambodia and Laos?

Thanks!

The only country giving you a visa on arrival (border crossing or airport) will be Cambodia. For Laos or Vietnam you have to get the visas in advance.
My advice would be to fly from HK to Phnom Penh with Dragonair (daughter of Cathay Pacific) and then get the visa for Vietnam at the Vietnamese embassy there. It takes 2 or 3 working days. The Cambodian visa is easy to get on arrival and you just need a form, a picture and 20 USD. The form will be distributed on the plane already.
I would prefer Cambodia over Laos. After 2 days in the capital get a plane to Siem Reap and visit Angkor.
Or if you like beaches more than Khmer ruins try Sihanoukville, just 4 hours by bus from Phnom Penh. And I hope the Vietnamese consulate is still in Sihanoukville. Once we got our visas there in 10 minutes instead of 2 days in Phnom Penh.

Visa issues first: You MUST arrange your VN visa in advance, It is not available at any border crossing. You can get Cambodia or Laos visas at most land borders and all international airport entries.

Whether to go to Cambodia or Laos depends on what you are interested in. If you want to see the temples of Angkor, then you'll want to go to Cambodia. Have no illusions that you can see the country in a week; in a week you could visit the temples and perhaps Phonm Phen or another location.

Laos has Luang Prabang, which is a lovely small town, the old cultural capital. Again, you can visit perhaps two places in Laos in a week.

Wolf, we were posting at the same time. Unless something has changed very recently, Lao visas are available at most land border crossings. The visas issued at such crossings are good for just two weeks, but since they only have a week to explore, that shouldn't be a problem.

kathie,
once again you were better informed than I was. Didnt visit Laos for 1 year or so. Thats the reason I missed their changing of regulations. Anyway, visas on arrival now can be obtained for Laos too.
But as far as I know there is no direct flight Hong Kong to Vientiane or Luang Prabang. So Hong Kong/Bangkok/Luang Prabang/Siem Reap/Saigon is doable. But a little bit much for 1 week only.

Wolf, I wasn't recommending both Luang Prabang and Cambodia! You're right, they would spend all of their time in transit. To get to Laos, it would require a stop and transit in Bangkok. With the DragonAir flight, it's easier to get to Cambodia from Hong Kong.

Laos is more for trekking and eco-tourism, as a general rule, and Cambodia more for Angkor Wat. Though, obviously, there's more to the country than just those two things!

Luang Prabang is a nice little town but have no mistake, it was very touristy. Once you got outside the town just a little it got much less touristy. If you wanted to, and had the money, you could hire a car and driver and explore the northern parts of the country. I ran across a senior couple who were doing this, with a car, driver, and guide, and they were just finishing up in Luang Prabang. They had a blast! No clue how they arranged it, though.

We got visas on arrival at the LP airport last week. $35US and one passport picture. Took about 5 min.

The main street in LP had about 2 dozen tour and travel offices (some looking more legit than others, to be sure) offering every kind of trip into the hinterland you could imagine. If you want to explore the countryside of Laos, just get yourself there and make whatever arrangements seem appealing.

Personally, if I could only do one (and that's all you really have time for) I would pick Cambodia. I loved LP, but I think it's a place you go after you have done most of the major sights in SE Asia. the temples in Siem Riep are a once in a lifetime experience.