I'm gonna do a quick little rundown of what it seems are the leading contenders, judging by the threads started.
First;
The Brewster. It is almost a national icon in Finland, and achieved a heckova kill ratio there. But, being either on par, or inferior in performance to the current F4F, I would guess it would be a hangar queen outside of AvA or scenarios(and possibly the EW, at least until the novelty wore off.)
The G.55-If you go to that thread and read performance stats, It would be a fighter plane that would hold it's own in either the MW or even LW. However, it would be exactly that-Just another fighter. We have plenty of those already.(P-51,F4U,Typh,Fw-190,ME-109,etc.)
P-39: Historically important(like the Brewster), Used by most of the allied nations, Not particularly fast, but Heavily armed. Not sure about it's manueverability, gotta see one from HTC before we could judge it. Might span all the MA's, but not sure about EW.
The HE-111, a bomber this time, has been wanted for a complete BoB scenario since the start. As far as usage in the MA, It would be useful in EW/MW for sure. Especially EW. If it's allowed it's historical ord options.
The B-25, which would span several models, Is kinda up in the air as far as usage goes, because it depends on which B-25 it is. The Earlier ones, such as the C's, would be used in the EW or MW for sure. The later Gun pack models could make quite an impact on the LW's, especially if it was the 75mm. version. Therefore, It depends on HTC as to which version we get.
A Yak-3, if modeled as the most manueverable fighter of the war at low lvl, as has been claimed, would definetely get usage, even in the competitive LW arena's. If it could outturn, or at least turn with a Zeke, but be about 60 mph. faster, this thing would be a monster.
The Japanese planesets have several proposals pushed forward, which while filling several holes in AvA and scenario planesets, would be hard to gauge their impact on the MA crowd. For example, the P-51B is a pony, performance is not very much different from it's P-51D sibling, but it does'nt get even half as much usage as the D. Why? Probably the armament and views. The same thing will apply to the Japanese planeset. The Ki-44, whilst being a good performer, was armed with 4x 12.7mm machineguns in it's most produced version. There were cannon armed versions, but whether or not this is the one we get, is up in the air. The J2M2 and J2m3 were armed with 4x20mm's...These would probably get more usage than their lack of manuverability would lead you to believe.The Ki-43, which would be EW, would have the weakest Fighter armament of any fighter in the game(2X7.7mm's for early models, 2x12.7mm's in ltr) and would be one of the slowest as well. But, It's manuverability and turning radius would be even better than the A6m's.
The ME-410, While seeming to be an improvement over the 110G, would'nt truly be a departure until fitted with the 50mm AT gun. Alot of incomplete data on this plane, concerning turning radius, climb, etc. This one is harder to guess at...But it would have about the same impact, gameplay wise, as the 110.
This list is by no means complete. We still have some of the aircraft listed by Pyro that aren't here. But, These seem to be the ones with the most supporters at the moment. The real problem with this list, is that we eventually could use ALL of them. The biggest problem with this whole voting process is the fact that we only get one.