Recon Pro. No way to hide from it and is pretty useful. Would probably be considered "overpowered" if Sleight of Hand, Scavenger and at times Blind Eye wasn't in first slot.
Honorable Mention: Hardline Pro- makes ASSAULT killstreaks even easier to obtain...You are a scrub if you use Hardline Pro with Support...Actually using Support at all makes you a scrub :carling:
Sitrep Pro. It's a great perk but I really can not be bothered taking the time to complete the challenges for Pro version, which increases the sound of enemy footsteps.
It was easy when you could just the Trophy System glitch, but now it is patched. Overall great perk if you never want to die from a Claymore or Bouncing Betty again.