I use Paralells to run XP, and use Tradestation from there. Fast, easy and rock solid backups. Run 2 screens and you have OS X on 1 and tradestation on the other.
I'm using FXCM java platform for MAC. So far it's been ok. Also, i think OANDA's java platform is not bad. But again I'm trading quite conservatively and don't do news trading or anything that requires 1000 clicks per second