As for why I am indecise between these two( Much as in the "Who has the worst cavalry" thread I made recently ), the reason is because these are the two only civilizations in the game that can counter all three default unit types( Archers, cavalry, and infantry ) using infantry alone( The Norse have Throwing Axeman against infantry, Huskarls against archers, and Ulfsarks against cavalry: The Atlanteans have Fanatics, Murmillos and Katapeltes against cavalry: Fanatics against infantry and Destroyers against archers. ). If you count Hersirs as "infantry units", as well as the Atlantean abilities to turn their human soldiers into heroes, this gives then the added advantage of also being able to counter myth units with infantry just to top it off.
As for why I think Atlanteans are just a little step above the Norse in the infantry department... To be frank, I think Fanatics are basically the best infantry unit in the game, so, here is the reason But since the Atlanteans are my all-around favoured civilization, this may be bias speaking. I am wondering on what would be your opinions on this, as well as if you think there is another civilization would deem as worthy of earning the cake instead.
As for why I think Atlanteans are just a little step above the Norse in the infantry department... To be frank, I think Fanatics are basically the best infantry unit in the game, so, here is the reason