Depends. I've flown Luftwaffe aircraft for 4+ years, and I'm not going to say one is inherently better than the other.
For knife fighting, the G2 is probably the best in the set. There isn't anything it can't do at least acceptably, and it can really mix it up if you have to.
Personally, I prefer the K4, but its not necessarily "better". It takes a higher skill level pilot to fly it to its potential, is harder to aim with, and is vulnerable to more maneuverable aircraft. But if you master it, you'll be able to out fight most others in the game, perhaps even those G2 sticks....