I have two Kimbers and two STIs. I placed an order for another STI last week.
Fit, finish, and quality of the materials is far better on the STI.
I haven't had any reliability problems with either the Kimbers or the STIs so that a draw I suppose. Kimber does use MIM parts and some of those parts, barrel bushings and slide stops in particular, are common failure items.
The bore of the STI barrels is FAR better than the Kimbers. My 5" Kimber looked like it was rifled with a chain saw - it shot all right but was prone to leading up pretty badly with lead bullets.