Which hero is better to choose?

Hello everyone, I just registered on this forum and have read many interesting topics here. I'm learning how to play as Necropolis, as suggested here: take Galthran, Izru, and Tanta, and create a lot of skeletons, etc. I'm currently playing against the computer on the Expert difficulty level. Could you advise me on what map size is best for Tanta, and where Galthran would be most effective? Also, what tactics should I use with Izru, and on what types of maps? I really need your advice.