There are many factors that you must consider before investing in a paintball marker that you will be satisfied with and will last.... don't approach buying your paintball gun lightly.  First, ask yourself how seriously you take the sport and this will help you decide how much you're willing to spend on the gun.  If you're a casual player who only plays every now and then, start off with something cheap, but of course reliable.  If you're on the other end of the spectrum, play all the time, take the sport seriously and maybe even compete, then a realistic military replica tactical paintball marker is for you.  Perhaps you're somewhere in-between?  

When starting out, a low end paintball marker will suit your purposes.  Most brand name paintball guns have starter models that are relatively cheap.  If you're not sure whether or not you will even like to play, you don't want to spend a lot of money.  If you're really unsure, it's best to go to a commercial paintball field where you can rent equipment; this is the lowest committment.  However, if you're a full on paintball warrior, nothing but the best will suit you.  These players end up using top of the line paintball gun packages - decked out with all the trimmings.  Perhaps a sniper rifle with a precision scope and bipod or realistic M4 carbine with an electronic trigger will suit your appetite. 

If you're in the middle, just make sure you get something sturdy, good quality, has a warranty that won't break your bank.  Tippmann is a great company and has several different models to choose from.  Their basic model guns are geared toward a younger player and thus are perfect for someone who is not looking for something that is packed with features.  They're also the most customizable markers on the market, so many players keep their Tippmann's and upgrade them with accessories as their skill levels increase.