Edit : Oh nvm, the pic didn't load. Let's see.. strong options include W!Tharja, Zelgius (tho I prefer BK for merges), Surtr and B!Hector. Sheena is really good when merged, but a bit costly to build.
I'm currently running B!Hector, Zelgius, Surtr, and Veronica and they seem to work alright. Need to get their builds down and figure out the Armor skills to stack.
Is an all armor team preferable to a team of three with a healer?
That depends on your playstyle, I guess. Personally, I don't use armors that much, but a thing people like to do is to stack 4 Ward Armors for a +12 Def/Res boost so there's that. If you're even using armors in the first place, might as well go the whole way