It of course boils down to play style. The only "tank" I actually like in this game is Dao, but that's beside the point. I have Kofi and Ardo at 35+ (Shell, Anti). My original thought on Ardo was, offensive tank, hench boss, I found that on paper he looks great...but fails in execution. The sum of his whole is just not greater than any other "tank". So if I could only pick my choice is Kofi.
Between Simo and Manawa is a much tougher call. If Simo had any other path other than Mana Spring he wins. I like Mana Spring (despite healing strike being ****)...but on Heavy armor warriors. Manawa can lead...but that can leave you exposed to heavy hitters in the arena. If I could choose only on I would pick Autopotion Simo in an extremely close call. (For the record Mana Spring Kwan was one of my original 35+ warriors)