I thought to save the other thread from being hijacked, but also to encourage some nice discussion. I didn't include
King's Bounty in the poll, although it was a predecessor of the series - let's keep it HoM&M clean
Also, I would encourage everyone to post their opinion why they find a certain game the best of all, like what does it have that the others don't and stuff like that. When making a choice, please take into account all official expansions as the part of the game, not a separate game altogether.
Finally, everyone is entitled to an opinion, so if someone thinks that HoM&M1 is the best part in the series, you may disagree, but that doesn't mean that either is wrong. Opinion in this case is a very subjective thing.