Alot of votes of KUL so let me be a contrarian.
BKK would get my vote. In fact that's basically what i did four years ago.
1) 30 days stamped into country on each return
2) great selection of flights to everywhere
3) train to/from the airport
4) centrally located within SE Asia
5) intangibles (food, things to do)
6) much more enjoyable than KUL
If you're working from a 'I don't care how much I spend' position then HKG would be my choice.
Also, let me suggest staying away from Air Asia. They are often not the cheapest airline (even though they are successful at representing themselves that way).