What's your budget? There are so many bargains out there at the moment, but your choice is dictated by how much you can afford. In terms of new gear, you can get (in some vague order of price) Proto SLG, Ion, PMR, Mini, Etek, all of which are great markers. But consider seriously buying second hand - the market is very cheap at the moment, so you can pick up last year's higher end guns for peanuts (much to the chagrin of those of us with a house full of old guns we can't shift!)
Above all try out as many different models as you can - every paintballer loves showing off their toy, so just ask around and people will usually let you have a rip at the chrono station with theirs. Look also at what the most people at your local site use - it's handy to have experienced owners on hand in case you have any problems with your marker.