Ive always found kydex to work better and be more comfortable than leather, especially if you sweat. I work outside year round, and have to deal with upper 90's, and high humidity, so I'm usually pretty much "wet" early on and for the rest of the day once the summer rolls around.
If youre in an office or climate controlled environment, and go from that to your air conditioned car, and then back to an air conditioned house, it really doesnt matter. Switch to living outside, and its likely to be a different thing altogether.
The advantages to kydex are, the holster and gun stays dry, and the holster isnt an irritant against your bare skin if your tee shirt should ride up. Wet leather rubs you raw, wet kydex just slides across your skin. You also dont have the chemicals used to treat leather to deal with. They tend to just add to the burn.
Leather gets wet, stays wet, takes for ever to dry out, and wont if you put it right back where it got wet in the first place. Once wet, your gun is constantly wet while its in the holster. Depending on what youre carrying, you can see where thats going.
I never got the whjle Comp Tac thing and always thought they built their holsters backwards. If anything, the leather should be on the outside, away from the body, not against it.