I like a lot of the historical matchups in scenarios. When you have historical match ups under somewhat realistic conditions, the fights can have a very different character than what folks are used to.
Here are match ups that I think are quite even and very fun, where the aircraft have different advantages and disadvantages that play off in interesting ways.
P-40's vs. Zeros
F4F's vs. Zeros
Spit I's and Hurri I's vs. 109E's
Spit V's vs. 109F's
Spit IX's and Typhoons vs. 190A5's and 109G-6's
Mix of P-51's, P-38's, and P-47's vs. mix of 109G's, 109K's, and 190D-9's