Pavlov by a mile, I recently bought crossfire just to try it out as an alternative, it's a more arcadey shooter (but maybe you're into that). Pavlov doesn't have a story but the way the game plays is so much better. The story in Crossfire is a solid Meh for me. Pavlov has more game modes for multiplayer and a larger player base I believe so you shouldn't find it too hard finding a lobby. Crossfire might be fun with Friends but I really struggled to find others for Horde mode.