Re: new polymer 45
I've been carrying a gen3 Glock 21 on duty for 5+ years now. Also bought a personal one and put many thousands of rounds through each. I shoot them well enough, and they ALWAYS go bang, but I never have cared for the feel of them.
Picked up a M&P 45 recently after falling in love with the feel of it. It is a really nice piece... but I don't think I'll be keeping it. The trigger reset really sucks (I'm just too used to Glocks in that respect I guess), the slide auto-forwards when you forcefully seat a new mag, and my thumb has a tendency to hit the slide release under recoil, often keeping the slide from locking back when empty. It shoots nice otherwise, and I really do think it's a *nicer* gun than the Glock, just not for me.
I picked up a gen4 Glock 21 a couple of nights ago and I really like it. The reduced grip size and new texture really has addressed much of my grumblings about the gen3 G21 grip. I'm still not a huge fan of the grip angle, but dammit they just work.
... the thing about it, for me, there is just absolutely nothing sexy about a Glock, at all. I don't get excited about them except for when I'm shooting them, simply because they perform so well. They're just boring. The M&P 45 on the other hand, man I think that thing looks nice, feels nice, etc, I just didn't take to it. I would try both if you can and see what works for you!