[Yellow]

Proyas is more intelligent than Saubon, and so provided he can be adequately steered, he is by far the higher prized of the two when it comes to matters of subtlety.

So, Kell never really sees them as "either or", he has very distinct roles mapped out for them throughout. We don't appreciate yet exactly what those roles are / were.

You are the fist that beats us.

[The Sharmat]

Is Proyas smarter than Saubon, or just much less angry?

[Monkhound]

Is Proyas smarter than Saubon, or just much less angry?

Saubon has been much more begrudging and impulsive than Proyas ever since TDTCB.
Proyas had usually been the one who wanted to do good, following Kellhus out of love which is what he gets, although in TGO is more of a twisted form of "tough" love. Proyas seems to notice the difference between Kellhus's and Akka's, as the passage with him hanging from the tree with Akka wanting to help him shows, but it's too late (as Kellhus points it out to him).
Saubon was a jealous self-serving man who followed Kellhus because of what he could get out of it. It's there since before the Battle of Mengedda in TWP.

[The Sharmat]

Everything Saubon ever did was to prove himself to everyone else.

[Monkhound]

True as well. The curse of the seventh son of Coithus Eryeat.

I find the nickname The Blonde Beast interesting as well. Was it in one of the Kianene passages in TPON that he was called thus?

[Madness]

Monkhound, I believe it comes in TWP as a name the Fanim worry about in an omnipresent POV when the Holy War makes it out of the desert and march on Caraskand.