I vote for...Vatsim! Sorry guys, but I've started flying alot more with Vatsim, and sure, IVAP is better and easier to use, but I don't think that gives us a reason to block all our events from it. WSSS is very very busy on Vatsim, compared to IVAO. On one day, 2 planes were inbound on IVAO, 20 on vatsim, so if you guys want a harder time when it comes to traffic, I'd put vatsim over IVAO any day. Also, the guys at Singapore VACC are always helping. I've flown to Changi about 5 times, and they're very very good. They're always very helping, and will probably love to come along for our event.
Finally, IVAO would probably have no controllers at WSSS, or VTBS. We could use our own guys, but I'm going to assume that it will be risky, as not many are probably familiar with the procedures, except Javier, and he doesn't controll on IVAO, so I'm all for Vatsim!