If you want to use it as a training tool to a 5.56 rifle, go with the S&W.
Just make sure it has a D prefix on the serial number. (Improved function blue action spring)
If you just want a cool looking one. Go with the "Colt".
I have the S&W and it is really useful if you want to keep the same functions/dimensions as a real AR. The only thing that is different is the weight because the M&P is mostly polymer and is quite a bit lighter than the real thing.
The best thing is that using cheap .22 ammo is that you can get good at SPORTS by the time you run through a whole box!