For the money, the Limited Edition Group Purchase (LEGP) from AR15.com can't be beat...
Damn, If it wasn't for CA, and their stupid laws, I'd have gotten one...
You essentially get a nice, functional Post-Ban M4gery. Of course, you'd still need to go out and spend a few hundred dollars stocking up on Mags and such, but the accessories package, discounted with the purchase of the LEGP is very tempting as well...
Consider this, Rock River is the primary manufacturer of the Rifle. They make great stuff, check out their 1911's.
If you tried to duplicate this with a Bushmaster, you'd spend another $100, easily.
A 16" carbine can be a fun plinker, and is definately capable of dispatching larger rodents, and predators out to 300 yards, although for distance work, I do prefer a 20" barrel, while the shorter ones are fun inside of 200 yards...
Hope this helps...