Although I like Glock polymer guns, but as I own and shoot all of them, my favourite polymer pistols to shoot in .45 are:
#1 - H&K Mark 23
#2 - H&K45
#3 - H&K USP .45
Although the MK23 is a LARGE pistol, it is one of the most balanced, accurate and 'coolest' pistols I've ever shot.
As mentioned above, the H&K45 is a very nice pistol to shoot as well.
I know I'll get "Flamed" for saying this, IMO I still prefer the USP over a Glock!
That's my 2 cents.