It all depends on your field and/or your team. Larger games will have teams set by camo type, so just get what your friends have, most everyone at big games (from my experience) tries to be John Rambo, so it's really not that hard to hide in the background when the OpFor has so many other targets of opportunity.
If you play smaller, pick up style games then you can get picky. Eventually you'll have 2-3 sets of camo and at least one ghillie.
Personally I'm stuck with ACU, Tiger stripe and a grass ghillie for the time being. I'd like to add Multicam and a woodland ghillie, in that order and then, maybe I'll think about A-Tacs or something more specialized.
As far as 'battle shirt' styles go, I really like the concept. For airsoft its awesome, even if they are the same price as the full blouse (typically). It keeps you cool, they're quieter, lighter and all around you get better range of movement.
Edit: FYI - they do make battle shirts in other patterns beside A-Tacs, so it's always an option with other patterns as well. I don't know about the older patterns like US woodland or US desert BDU styles, but they make them in Multicam, ACU and woodland/desert MARPAT as well as solid colors. I have also seen them in the British DPM as well.