The question - best fighter in Eastern Front, 1943. Kursk battle timeframe. There is lot of discussion on western front. Really eastern front was more important in 1943 until year end, even in air.
I believe best fighter was La 5FN. It is very fast, more manouverable, great climb. Speed - greater than Luftwaffe fighters where fighting occured.
Aircraft had two excellent 20 mm Shwak cannon. Also, good visibility - advanced solution, fighter had clear rear armor of armor glass.
Rate of roll was very good. Probably as good as Fw 190A. Reason - La 5 ailerons greater in relative area of wing than any other. Negative was greater working load of pilot - most system manual.