Not counting the K4, the G2 is the best IMO.
With Gonds on you can still turn fight at a respectable level and pack a serious punch. With out the Gonds the speed, climb and turning ability make for a very compatent fighter. Even vs. late war rides. The G6 to me has the best rudder out of the 109's and really helps with gunnary. The F4 is the best flat turn and burn 109, but is slow. The G-14........well,,,,, might as well fly the K4

(rarly DT in any 109,,drag performance hit is not worth it)
Respectfully
Jeffn