Actually a funny question because neither could stay on the other's six for long. If the 109 was tailing the 205, the 205 could simply make a steep dive and make high-speed maneuvers which the 109 could not follow. In fact, the 205 turns so well at high speeds, he may be able to wheel around to the 109s six IF he waits until he's, say, well over 400. At that speed, the 109 won't be able to turn at all. If vice versa, again a steep or shallow dive and the 109 leaves the 205 in the dust. However this assumes a nearly equal E state at the outset. In the long run, as soon as the 205 runs out of altitude (he's really only got his high-speed maneuvering as a clear advantage), he's fighting a losing battle from which he can not run.
Be that as it may, they're both thoroughly offensive planes and love to take the initiative against enemies. I myself prefer 205s because I love high-speed maneuvering and prefer to keep my speeds up as speed is both offensive and defensive. However, if you want to stay fast (and you do with both these planes), you need to pick your fights carefully. If the bandit is trying to lure you into a turn fight, you really have to give up an off-angle gun attack to regain E.