I think the AI works best on smaller maps. They make their moves much faster as there are fewer numbers for the AI to crunch at purchase or on movement.
Perhaps making a dual challenge would be fun. First Allies then Axis. With some goals set up.
I think 1942.2 (world war II v5) is a solid map for a challenge. There is a 1942.2. Tournament going on right now, so that may help to garner some interest.
If you want another “blast from the past” might try AA50. ;)