I had no problem using ATMs in Vietnam, Cambodia, Laos. Phillipines is a different story, very hard to get ATM access outside the main tourist haunts, but I'm asssuming thats not on your itenerary.
Never used travellers cheques, think they are as much hassle to get cashed as looking for an ATM is.
Very handy to have some US dollars stashed away in SE Asia though, especially in Cambodia, where it is used almost more than the local currency, and expected by tourists. The ATMs dispense it though, so shouldn't have too much trouble.
Most accommodation providers and restaurants don't take credit card, so you will need cash at all times.