I'm not a fan of 22LR AR pattern rifles. (For the record I own and H&K model 516 that I got for practically nothing)
But I'll give everybody that owns one a few of my observations of the M&P 15-22 compared to all the others out there.
This would cover the Mossberg, Hammerli, H&K, and a couple others I can't think of at the moment.
One of the best things S&W did was to build the fire control systems nearly the same as the full size AR pattern rifles. The charging handle bolt and carrier dis-assemble like the big boys, and is super easy to clean and maintain.
With the others, they require nearly tearing down the entire rifle receiver and fire control from the frame, and cleaning them appears to be a royal pain. I've had a couple of my customers that bought the other brands come in and replace them with the S&W's because the operate the same as the full sized rifles and all of the controls are exactly where they should be. When teaching a youngster how to use an AR, the S&W M&P15-22 is the rifle I recommend, far above all the others.