It all depends on the number of friendly and enemy secondary towns. If we have a classic distribution, like a starting town + 2 enemy secondary towns (or something similar), and some dwellings, then a Necromancer (leveling up on low-level fortresses) is a good choice.

But why, if there are secondary towns, should a Necromancer use zombies instead? It's much more convenient to place a level 4 building for vampires or, at worst, a level 5 building for liches – that's clearly more useful. As for humans, I would still bet on them because with a few trainings and mass upgrades to cavalry, they can tear through poor Paladins, not so much with speed, but with their numbers... So, in my opinion, in the late game with additional (with any, actually) castles, the Necropolis faction crushes everyone, and then come humans and Inferno (one with training, the other with summoning), and the rest, well, probably except for Gnomes, are not viable... :)