I want to get a few travelers checks for my trip to Thailand, and I have the choice between Visa or American Express. Is there a preference? Also, how about denominations? I was thinking 100's or 50's. Thanks

Fro T/Checks doesn't make any difference, 100's and 50's fine, remember though that you 'have to' take your passport to change t/checks.
I would honestly stick with ATMs and cash, good idea to have T/checks as a safety back up but I wouldn't bother actually using them on a day to day vasis, they are a safe back up though, but have at least 2 ATM cards, preferably from different issuers ( Visa / mastercard ), the old tips is one in the safe and one on you, if 2 traveling together have one each but always have 1 back in the safe. I actually still use old fashioned cash a lot when traveling, USD 500 will take care of a lot of spend and if you change a couple at a time chances of loosing any are pretty small, I always think that I would sooner have 100 or 150 bucks lifted from my pocket than a credit card!!

Just to add to the above, T/Checks can really only be changed at a bank exchange. Exchanges are plentiful in Bangkok, and many are open on Saturdays and Sundays. Shops don't take T/Checks at all, and of course you NEVER change money at a hotel. There's an extra charge to change T/Checks, so in the end it's quicker and easier to change cash.

If you bring US currency, bring 100's only. You pay more to change 50's or smaller. Try to get new bills as well, since they can be a bit fussy about older ones.

I also use the ATM for most of my travel cash these days, but check your bank's charges before you go. Some can really penalize you for using their ATM's overseas.

Thanks for the replies. I guess I need to make my question more clear though. I can either get Travelers checks that say 'Visa' on them (Visa brand T.C.), or T.C.'s that are American Express brand. Is there an advantage or disadvantage to either brand. I kind of blew it on my ATM card as I don't have enough turnaround time to order one from my bank. Next time I travel I'll have one.

No advantage. I always use Am Ex because I find their customer service far superior. I once was in turkey and both my checks and my friend's checks were stolen. Mine were am ex and her's were visa. I got my replaced instantly and with no problem. She had to go through much more and it took at least a day or two longer. Based on that I stick with Am Ex.

I just take cash and a credit card for backup. ATM charges are high for some banks so I skip the ATM route. I keep a security wallet. Keep some in the security wallet and the rest I keep in the hotel room safe. This has worked well for me over the years for all of my trips.

either is fine...i have changed checks at tiny hole in the wall exchanges, i.e. non banks...no problem and a great rate...

last time my son took visa and everywhere we went he had to have his passport plus he never got a good exchange rate from the banks. We did the cash and car thing kept it in hotel safe and just took what we need for each day... Not wise having to carry passport with you everywhere in asia pick pockets abound, the only other opption is run back to your hotel after you have exchanged and put your p/port in safty deposit box. Gets a wee bit tiresome that hope this helps.

I never use T/C's. A lttle cash and CC for use at the ATM's. Note: AMEX now has a TC Card which maybe a better option than the actual checks.

Thanks! I got some Amex traveler's checks and I have a credit card and some cash. I appreciate the help!!

If you have an AmEx platinum card, you can cash a ck at the AmEx office (Ari skytrain stop) for up to $10,000.

BTW-- I just checked and AmEx charges 1% less on foreign transactions than my Mastercard and Visa does so I will be using it whenever possible to charge.