I have a glock 21. I love it. it doesn't shoot as nice as my 1911, but it's 13+1 capacity is hard to argue with. The M&P is one or two less, correct?
It is a big, clunky, chunky, brute of a pistol, but there are times that exactly what you want.
The only other double stack 45 I would consider right now is an FNX Tactical 45.
HK's are ok, a MARK 23 would be cool, but they're like unicorns....