I do not know yet. I need to discover the ideal tactics for each. My choice will initially be towards a gang that has a chance of survival with a maximum of basic figurines. I don't paint very well so I practice with miniatures I bought second hand and a lot of them are from Battle.
I obviously already have roleplay preferences: skaven, human mercenaries, vampires, witch hunters,
chaotic followers, dwarven hunters, and Sisters of Sigmar. The presence of these gangs in the streets of Mordheim seems much more logical to me.