I think Banner will prove to be #1 in terms of smarts in the MU.
it would make sense of the Cho thing about a part of Banner always calculating the angles and trajectories to prevent Hulk from causing accidental deaths when on a rampage/in a throw-down.
"Banner Tech" has consistently been pawning Reed (and recently Doom too!), ever since Banner was forced to resort to using his brains rather than hiding behind The Hulk...
anway, as The Hulk once told Juggernaut: Hulk The Smartest One There Is!
seriously though, prior to the focus on Banner, I would have put Doom #1 (more of an aggressive personality, so he pushes himself more and so finds new, higher levels of ability), Reed second (too removed and engrossed in abstractions to fully utilise his brains - too one-dimensional) and Banner 3rd (from stuff prior to FOTH).
in DC ... I go with Bruce ... Socrates was a pederast too! ✅