All depends on what kinda paintball your going to be doing. Speedball or Woodsball.
Theres many things to consider aswell. In my opinion investing in a good tank, mask, and hopper before you buy the gun is always the best route.
If your going to be doing woodsball i would suggest a Tippmann 98 custom or the A5, for beginners. It is a very reliable gun and can take a beating. Also they are very cheap and easy to clean, and you can custimize them alot.
If your going to be doing speedball and are not looking into spending alot of money I would suggest the Dangerous Power G3 (I have used this gun and it is very good for te money you spend). Its an inexpensive gun but performs very well and can keep up to some of the higher end newer guns.
If you need to know anything else let me know.