Official commentary to the new screenshots has been posted, confirming the name of the two factions which have been appearing in the released screenshots:

Check out 9 new screenshots of Heroes of Might and Magic V in the gallery. These ones showcase for the first time the Haven town and highlight the most powerful creatures of the Haven and Inferno factions.

No surprises there.

(Note: these are the two factions which will appear in the demo of the game).