I'm looking to add a semi auto handgun to accompany my 642 carry gun. I have been looking at the G17 and 21 Gen 4, but my gut is telling me to take a look at the M&P 45, XDM 45 or maybe a used USP. I'm leaning polymer too. I have no interest in a 1911. What can you tell me about the non-Glocks such as the M&P, XDM, HK, etc as they stack up against the Gen 4 Glocks?