all resources are approximately = 250 gold
1. Tower 31800 (30800 + 4 gems)
2. Castle 31080 (29580 + 6 gems)
3. Conflux 29500 (28500 + 4 mercury)
4. Inferno 29090 (28090 + 4 mercury)
5. Dungeon 28205 (27205 + 4 sulfur)
6. Rampart 27620 (26620 + 4 crystal)
7. Necropolis 27420 (26920 + 2 mercury)
8. Swamp 27160 (26660 + 2 sulfur)
Stronghold 25530 (24530 + 2 crystal)
I would like to draw attention to the Tower, Castle, Necropolis, Rampart, and Dungeon, as I think they are more interesting.
From this it follows that the Tower is the most expensive, and moreover, the Tower and Dungeon are the most expensive in terms of building units. The Tower requires a huge amount of gems and many other resources, such as crystals, mercury, and sulfur. The Dungeon requires a lot of sulfur.
The Stronghold also requires many resources for construction - a lot of wood, stones, and crystals for hippogryphs and cyclops. The Rampart requires a lot of wood and crystals. The Necropolis is relatively cheap in this regard, and the Castle is a little more expensive.
Castle - level 1 and 7 are the strongest. The Halberdier can only compete with the Centaur. The Champion is in 3rd place, the rest of the units are above average, the magic is above average, the stable is a good helper in scouting.
Tower - level 6, 2nd place. Many archers and magic. The vast majority are not contenders for the first ranks in combat, but there are no weak units.
Dungeon - a lot of magic and useful buildings (experience, portal, artifact merchant (as in the Tower), bombard 2nd level and 2 good archers), a strong 7th level.
Necropolis - undead! Levels 4 and 6 are the strongest, good magic, a good archer, the rest of the units are average.
Rampart - good defenders, unit 3 is an excellent archer, level 1 is fast and not weak, all other units are above average. Good magic, useful buildings for developing the city.
So, I would give first place to the Castle and Necropolis, second place to the Tower and Dungeon, and third place to the Rampart.
But, as they say, in good hands, each of these, and indeed all the other cities, will find its superiority, because the balance in Heroes is excellent.