If I have all orange combat heroes and all three heroes unlocked in all Apc's. Which combination of..

This depends on what you are trying to do. For attacking zombies generally a formation of fighters, vehicles and then shooters works well as it has a good all round attack. If you want speed then having all three rows as vehicles makes your APC travel much faster.

If you are taking DoomsDay plots/buildings then all fighters gives a much higher destructive rating. If you have unlocked and upgraded the war room buildings then you will have buffs for having all the same type of troops in an APC.

For heroes the best ones are the ones you have managed to unlock / upgrade the most skills on. There are also some heroes that have special skills that only work with certain troop types. I.e. when they are leading vehicles for example. Make sure you place them with the correct troops.