Auto-translated
I definitely voted for the Barbarians and the Swamp! But you can also add another faction.
I thought that with each new installment of Heroes, the number of castles would increase, but that's not entirely true!
Having 8 castles is good, but more... well, ten is possible, but if there are more than 10, then the factions themselves might not be as interesting (diversity isn't infinite, and it's hard to think of and design everything...
The third part is still the best in this regard... at least better than the fourth, and the fifth... the fifth (if with the addon) is probably not worse than the third, and maybe even better....
I just haven't installed the addon on my computer yet (that's why I haven't seen it).