I don't own either (yet), but my next purchase is an STI. I'm not sure which model yet, but I know it's STI.
For every positive report on a Kimber, there's a negative. For every positive for STI, I find almost no negatives. I believe that is because of service AND quality.
Yes, anyone... even Glock can make a bad gun, but it's about (1) how frequent and (2) how do they handle it. Based on my research STI blows Kimber away in both categories.