[Quovatis]

From the list, it's Aircav, but overall I'd say the cert system or hit detection.

Why Aircav? Even relatively noobish pilots can get large killstreaks. I was told repeatedly by "elite" pilots that I really suck as a reaver pilot. I could easily get 40-0 streaks with a reaver. Since I apparently suck, the better pilots do even better I presume. There is no other weapon/vehicle that you can consistently get such a high k/d ratio with. The reaver is just too powerful. It's good against pretty much everything (infantry, armor, and air!), and the only thing that can reliably take it down (the wasp) is hated to hell and back, even though truly skilled reaver pilots can take on a wasp and win if they know what they are doing. The reaver should do almost no damage to infantry and air, and be anti-armor only. That way you need mosquito and wasp escort to be effective instead of being a one-man army.

I don't see the big deal with BFRs. After they were nerfed to hell, they are pretty useless. They take forever to kill anything, and can be killed by one agile with mines and a jammer. The NC particle cannon is the lone exception, being completely OPed.