Jugs, Mossies, GV's, 110's Early war stuff, 1940,41&42, especially for IJN. Anything unique that would simulate real world situations. Maybe more targets or adding small targets of opportunity to attack.
I feel that generally, with the exception of the large U.S. bombing raids, and late in the war, the defending side of an engagement would usually have a numerical advantage. This numerical advantage was offset by the ability of the attackers to concentrate their forces and to use suprise and attack when the enemy is least prepared. This unique kind of cat and mouse game is something that Squad Ops is particularly capable of recreating. I think that even events that are not historically accurate, but sort of "what if" type scenario's would be fine to run so long as it provides an enjoyable framework to conduct squad operations.