I am a bigger fan of Crossfire. Not only is it fun to deal with both bots and human opponents, the map variety helps keep it from feeling redundant. While Blitz is fun with friends, it does start feeling very samey-samey. After the Devs are done with their much deserved break, it would be nice to see a new Blitz map, just to add some variety to it.
Crossfire. My friends and I tore through all the Blitz modes in an hour. Scramble was insane but, I don't think I'll ever want to complete that again.
This ^. Love Blitz also, things can get hectic and sometimes you just want a break from crossfire. But fighting it out with real players is tops IMO.
Blitz was fun until I completed the Achievements, and is still pretty fun for Local Co-Op if I get frustrated with Online play, but for the most part Crossfire is ftw. Each game is different to a greater extent than Blitz, making for better replay.
I play as an Assassin and Gunner, I got to round 152 on Blitz, but i do love Crossfire more. Haha. Blitz is fun though.