OK, I know, I know. "Best" Glock is really a subjective issue, but, for me, the Glock 21 is, by far, my favorite Glock. Love it. Had a good range session with it yesterday. Here's an introduction with firing demonstrations.
Reasons I love it:
The large grip, I have big hands and I get a great purchase.
The site picture/radius, for me, is fantastic.
Trigger is my favorite Glock trigger, better than my other Glocks.
.45ACP - 'nuff said.
Great capacity: 13+1