if u're not averse to flying, i think singapore or vn wd be equally convenient. at least 2 carriers service each route. i used to fly btwn saigon and bangkok regularly and the flight is only one hour; i'd imagine hanoi or singapore wdn't be much longer.

the destinations are vastly different, however. singapore is even more modern than bangkok, w/ highrises, air-conditioned malls, a subway system, worldclass department stores and every other person walking ard w/ a cell phone clamped to his ear. it also has interesting ethnic neighborhoods, which vn doesn't have.

in vn, hanoi is more old-world than saigon. i wd write off saigon for this reason. hanoi does have more french colonial flavor, more communist flavor (in bldgs, dress styles and attitudes) and fascinating shopping streets that specialize in one thing each. it's a pretty city w/ accessible lakes and parks. if u want somewhere that will contrast w/ bangkok, i'd go there.