paddy, do you know which kind of marker you are after? as there are two distinct types in paintball, electro's and mechanicals. the electronic ones allow for faster rates of fire and are less likely to break balls inside the gun (thanks to good ol' technology). the mechanical ones generally shoot a lower R.O.F but in most cases easier to maintain.
really it is split up like this:
electroes: when they work they work better then most mechs by a long shot, the only problem is due to them being electronic there is more stuff inside which can go wrong
mechs: most mechs are like cockroachs, they never die. i've heard of people throwing tippmans and BT's into ponds, then picking them up and fighting on. but you sacrifice ROF for this durability.
people will say that they did ... with there ... but it is fact that mechs last longer than electroes, and that electroes shoot faster than mechs. (nearly all of the statements are void in the case of 'mags)