The Spit IX is generally one of the best fighters for the main arena. You can E fight against the true angles-fighters (spitV, a6m, hurri), and turn against the E fighters. The combination of 2x50cal and 2x20mm hispano is great, and packs a pretty good punch. The balistics are similar for these weapons, so if you hit with one, chances are you'll hit with the other.
The LA-7, in my opinion, is the best fighter for the MA. It is the ultimate low-alt E fighter. It truely excels at E fighting, even against other E fighters (109's, P-38's). The elevators and ailerons are very responsive, so you can make last second adjustments for your shots without losing it. Considering the top speed and acceleration of the LA-7, it turns exceptionally well. The closest low-alt comparison is the G10, which has a similar zoom climb, acceleration and top speed, and the LA-7 turns quite a bit better than the G10, especially if the misguided fool is flying with gondolas (as many people do).
I also forgot to mention that the LA-7 has the highest top speed on the deck of the un-perked fighters.