Hong Kong, Kuala Lumpur or Singapore?
 

What's the best place for a short trip?

Hong Kong definitely. Great nightlife, and there are wonderful things to see also. For a quick trip, I would try to take a day trip on a junk to one of the small islands, I would go to Sha-tin in the north to the temple of 10,000 buddhas, and also eat at the huge floating resturant in the middle of the bay (Can't remember the name of it right now). Sydney market is also fun.

KL is fun also, but Singapore is just too uptight and restricted IMO.:2 cents: