Im fixing to have one I just cant decide which one.

Glock 34 (9mm)
Shootability and ammo cost are a major plus here and I really like my G19 so this would compliment it nicely.

Glock 41 (.45)
This one has a thin slide like a G17 and is a full size 14rd .45 - nothing more to say..

Glock 40 (10mm)
If Im going longslide why not go all out? This is the modern day Dirty Harry pistol.
6" 10mm Auto, 16rds, simply awesome.