I tried Prep + Prime a few times and it made me feel greasy very quickly, and the fact that it has little pearl particles in it don't flatter oily skin at all.
If you mean Smashbox Photofinish primer, that one didn't do much for me either, having oily skin. Contrary to what many have stated, it's not oil-free (mineral oil free, yes). I like the Photofinish Light primer, which has more of a lotion-like texture, but is very smooth and stays matte, it's 60% water and oil-free. I also really like MUFE All Mat primer, which has a similar texture to Photofinish, but not as slick and it's also oil free, it has incredible staying power, but it's a tad overpriced IMO @ $45.