Best is relative to your own goals. For me, returning to base is always my objective when launching, so durability plays into my choice as much as performance and firepower. So I prefer an air cooled engine when attacking bombers.
Late War - I choose the Fw190A-8 as it offers a good blend of qualities mentioned above.
I don't fly allot of Early or Mid but would think the Bf110C, Fw190A-5, and Hurricane-2C would be good candidates.