October is the most difficult month for beaches in SE Asia mainland. Let me suggest that you start by choosing what is most important to you.

If Thailand is at the top of your list, then devote enough time to see some of it. The idea that you want to see three countries in two weeks is... not a good one. Logistically, you can do it, but you'll have no experience of the places. If you can make it three weeks, you have more options.

For a first Thailand trip, I'd suggest time in Bangkok, some time in the north, perhaps the Golden Triangle area, and if you want a beach add that in. If you have three full weeks, I'd suggest a side trip to Cambodia to visit the temples at Angkor. If you choose to cut the beach because of the weather, you might substitute Luang Prabang, Laos.

If the rain puts you off, opt instead for Singapore and Indonesia. They are affected by different monsoons, so the Bali weather will be good. Again, I'd suggest three weeks if at all possible. Indonesia is vast. For a first trip I'd suggest Bali and Java.

Take a look at www.weatherbase.com to get an idea of the typical weather in each location you are interested in.

a foray to singapore, or bali or both might be nice..

I agree Angor should be after the North of Thailand. You might want to locate a firm that might bbe qualified to take you to visit the trbis north of Ching Mai and the Keron spread out just south. Very interesting. If you want culture I might suggest Jojgakarta in Java with their amazing temples. We used a guide who is excellent wiedyantara@hotmail.com. He can take you on some hiking on the still active Mt. Merapi volcano up to 2/3 mile before the peak.Further he can show you villages that arethroufg backs to the Indonesia of 1920-1930's. In Bali their are several oppertunities for hiking off the main roads to lovely waterfalls, They are not large but are 30 fy and serene.Singapore we found to be worth 2 days of sightseeong but not much more, in our opinion.