Alright, fine, play as the Tower then... But in a one-on-one battle, the Castle will completely crush the Tower... It's been tested. There (in the Tower), you only have Mages, Nagas, and Titans – they're good, but everything else... Ugh....
Compare all the creatures of the Tower and the Castle (not in the usual way, with all skills at level 1 and no magic), but as a level 20 Mage vs. a level 20 Knight... All the Castle's creatures will have decent defense and attack (and that's all I need), while the Mage casts one spell and spends the rest of the round watching his army get turned into dust... :) You see, in the Castle, both the Priest and the Knight are warriors (well, the Priest is a combat mage, but that doesn't change anything), while in the Tower, you only have Mages and Alchemists (a parody of a Priest...).

Well, you know, I wouldn't say that! Honestly... The Castle will win against the Tower mainly because of its faster development in the early game – but if you do it the way you suggest – level 20 vs. level 20, with troops for the same number of weeks – then it's far from certain that the Knight will win, believe me!!! You can cast a very powerful spell – like berserk half of your army – and what will you do? Go make a great explosion, a meteor shower, a chain lightning spell :D And just something massive, like a slowing spell – and then comfortably shoot down all the Knight's troops! Archdevils are certainly strong creatures, but there's a way to deal with them – Nagas, for example ;) In general, your attack/defense won't help either :) Besides, you can reduce these parameters with spells ;) And in general, it all really depends on the player who controls the army. It's really all about him!