Safariland. I absolutely HATE the Serpa! We were training some FAST Marines in Rota in 2008 and they had a mixed bag of Safariland, Serpa, Bladetech, and G-Code. Hands down the Safariland performed best. (By the way, I'd take training Marines over boogs anyday. Highly motivated, quick learners, and a good bunch of guys overall.) I tried the Serpa and absolutely HATE IT.
I like the fact the Safariland's holster is lined. I prefer the ALS locking system over the Serpa's flawed design. The Safariland is capable of being moved from waist to PC if you buy the quick release kit.
I wish they would make the light area as modular as the M92 Burrito holster in regards to the light. I've never messed with that holster, but like the concept of being able to adjust it for a pistol with light or no light.