Search and Destroy............................Because it you get 500 when u plant or defuse.................if you get you 500 points.............so i say Search and Destroy
You can see on the leaderboards points per minute (average) and search and destroy is highest for nearly everyone. But its also harder to do challenges in search so that or demolition is probably a safe bet
HQ has been working for me. While I have only played 57 games (and won them all), I am already lvl 35.
It has been no secret that S& is the very best if you are average or better at this game, but HQ is also fun, while S& tends to get a bit boring.
I am averaging about 5000xp per game + Match Bonus + Challenges + Contracts.
No, free for all is the best. You get 30 kills every match, if you win, which is wayyy more than what you get on any search and destroy. Demolition may be better, but from my experience I level up after every match I play on Free for all.