Between the two, go with the M&P. Among the entry level ARs, they are at the top, or right at it. Btw, they are known to hold up to the Tactical Response "Fighting Rifle" course. That course requires 1,500 rounds in two days.
Btw, Gander Mtn sells ARs, and sells the M&P. Thats where I bought my AR. There are 2 (I think) gander Mtns in KY.