Re: Colt branded M4 Carbine model .22 caliber rifle
I own both the Colt/Walther M4 22LR and the S&W M&P15-22LR. Both are very good guns. Colt is slightly heavier and feels more solid, while the M&P15-22 is very light.
Accuracy wise, they are about the same, both will hold 1~1.5 MOA depending on the ammo used.
Reliability wise, both of them works flawlessly, with only 1 or 2 misfire in a case of 500 bulk ammo. I suspect the misfire to be caused by faulty cheap ammo.
ease of use, M&P15-22 has an edge here as it is much easier to disassemble and clean. but both guns run fine a little dirty. I've pushed 1000+ rounds with out cleaning, a little CLP and they works fine.
They're both nice little guns, good fun at the range or a little bunny hunting. I've had ruger 10/22 as well, and I personally I think you should get all of them. Can never have too many 22LR in your safe.
Peace