I have always been in the 109 camp, not because I think it is a better fighter, but because of my "emotional" feelings for it.
My honest belief is to decide which is better (Spit/Bf 109) is not an easy task. It is not black and white. I believe these things:
1. Both aircraft traded "superiority" over each other throughout the war.
2. There are just to many factors involved to just go off of "paper stats" (granted most of us have nothing to off of more than that).
3. Both aircraft had their advantages and disadvantages (as any great warbird does).
4. The "better" aircraft was the one which had the pilot that could get the most out of its advantages. That pilot would win the fight. Take a Spit with a good pilot and a Bf 109 with Adolf Galland and chances are the 109 is going to win. Now take a Spit with (Insert your RAF Great Pilot) and put a good pilot in the 109 and chances are the Spit is going to win.
I do however believe the following things as well:
1. The Spitfire was probably more forgiving.
2. The Spitfire was probably easier for a novice pilot than the Bf 109.
3. The Bf 109 was at the end of its evolution. I don't believe you were going to get much more out of the Bf 109. I also believe the Spitfire was at the end of its evolution as well. Having said that the days of the Piston fighter were coming to and end. You were not going to get much more out of "conventional" piston aircraft.