My vote is halo and not because I don't own an xbox.
Master Chief is a pretty generic character as is the game's plot, but no one plays FPSs for the plot, they are played for the rush. But that is the thing, Halo has no adrenaline rush. Regenerating shields competelu ruined and quickness to the gameplay. Make a kill? Go run and hide.
Plus in the first halo the pistol (with zoom) was the beat weapon in the game for multplayer. It is the weapon you started with, it did great damage and you could zoom for easy headshots. You should not have a seemingly weak weapon be the best as it sorta ruins the point of the other weapons. Also, regenerating bonuses like the uber shield can make the deathmatches pretty unbalanced (though many games have this, sadly, with no way to make those items 1 time spawns)