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Centaurs are quite strong, adding elves and the development is going well... Dendroids are a terrifying force... eight of them per week is too much... but they are "balanced" by pegasi). Unicorns are nothing special, and the dragons are generally tolerable. In the Castle, the only useful thing is the treasury... otherwise, the Castle is not outstanding in any way... Elementals are still the best anyway.
And the treasury is always useful on large maps.
So, Rampart rules!!!
Added 10 minutes ago
But it doesn't need as much ore as the Castle :(
In fact, you need at least 100 ore for the Rampart! And sometimes even all 130.
(just the dragons need 60, and that's without mage guild, etc.)
But 50 is enough for the Castle.