help picking the right gun!!!

a bunch of us are looking to get into this hobby.
we've all done paintball, and had bb guns as kids
how do i know what kind of gun to get?
im not looking to spend hundreds of dollars
just get a decent gun that will work with minimum
problems and minimum upkeep costs.

i was looking at a M4/M203 combo from Boyi D-boys
it doesnt look to bad, electric powered, (the 203 has
a spring/shotgun set up underslung)
always liked the way this gun looks, but im not really
sure what to look for, theres like 19 different M4's out
there.

whats important