IMO on the paper the spitfire has got all the cards
But in an event the 109 is much reliable in his flight behavior (no flat spin), gun package, and of course I'll mention the damn gravity fed carburator 
In a one on one it is easier to exploit the strengths of the Spitfire Mk I than of the Bf109E-4. The Bf109E-4's guns are better, but it has more trouble bringing them to bear on the Spitfire, which mostly eliminates that advantage. In a many on many the fact that Hans has trouble getting his 20mm cannons on Robert doesn't mean as much because while Robert is working on getting Hans, Gunter can get Robert and do so a lot faster than Robert can get Hans or John can clear Gunter off of Robert. One on one fights are not a particularly great indicator of battle effectiveness.
Now, the Spitfire Mk I and Bf109E-4 are so close in overall capability that even in a battle situation either side is capable of triumphing. For a more extreme example look to the A6M2 vs F4F-4. In a one on one the A6M2 utterly dominates the F4F-4, but in a many on many the A6M2s have almost no hope of winning, at least as modeled in AH.