I have owned both. I kept the Core 15 as my AR 15, and now have an M&P 10 in place of the M&P 15. You cannot go wrong with either the M&P 15 or Core 15. After 1000's of rounds through both, neither of which ever had a failure or malfunction of any kind, I believe both to be equal, and incredibly worthy and reliable rifles. I liked S&W enough to but an M&P 10 over a Core 30, but that decision was primarily price and resale value driven, or at least my perception that the S&W would hold its value better.