Practical?

I'm debating between an m4 or an m16... what are the advantages/disadvantages of either/both?

battery- m4= small connector (typically) m16= large connector(and large battery)
length of barrel in the m16 is going to be longer so there may be more accuracy depending on the brand (Kwa m4 would be more accurate than JG m16 for example)
So the m16 is better for field use and for cqb that doesn't have small rooms
then the m4 is better for cqb and close range, although the m4 can be upgraded with a tbb and some gearbox parts to make it close to, if not as, effective as the m16 at range.
What it really comes down to is the length of the weapon, do you operate cqb or field more.

Ya, although I would upgrade the tbb in the m16 if i were to get it. I play field more, but I go cqb sometimes, and I don't want it to be a hassle with my m16. And I'm comparing G&P M4 vs. G&P M16A3

M4. It's a great compromise between short and long ranges and it's shorter length will make it more maneuverable no matter where you're playing. Also, if you find you need more barrel length you could always put a barrel extension on or toss an upper with an M16 barrel on it.