The needler has the fastest melee recovery time in the game. This is easy to exploit in many situations.
1) If you are dual wielding needlers, hide around a door frame and wait for someone to come by. Just before they enter, Twitch-fire both of them, and as soon as they enter the room, melee like mad. This will instantly kill most people and can actually out-speed the plasma-pistol/smack combo 90% of the time. Especially potent on Lockout.
2) If you are single-wielding, use the SMG or any other weapon, then run around a corner, switch to the needler, and nail them with a couple needles followed by melees when they chase you. Once again, more effective than you would think.
3) Camp the rocket spawn on Beaver Creek. Get dual-wields, hide out where the magnum is, and jump anyone coming up the ramp from the base with technique 1 or hop on and beat down people coming up the big rock.