> S Tier
Juniper Sr.
Underrated as fuck, he's a cool old guy and is the right mix of knowledgeable and sociable, I suspect Sycamore and Kukui's personalities were intended to follow on from his but fell flat.
> A Tier
Rowan, Juniper
Rowan and Juniper interact with the player just enough that it isn't annoying, Rowan has the superior personality imo since he's a lot more collected and stern making him a good authoritative figure whereas Juniper is somewhat bland by comparison.
> C Tier
Oak, Elm
Vanilla as fuck, don't really care about either of them but at least they're not intrusively annoying.
> D Tier
Birch
Does more in the plot than the previous two but not in a positive way, Birch just feels like a floundering idiot in comparison to the rest and it honestly makes me wonder how when you have more competent Professors like Oak, Rowan, Juniper, Juniper Sr. & Sycamore that Birch could fit the role.
> E Tier
Sycamore, Kukui
Just annoying, Sycamore is marginally better because he doesn't appear every five seconds like Kukui does, Kukui also takes some of his traits from Birch making him more of a pain to deal with. The thing about Sycamore though is that he is redeemable, you can make a good character out of what's present, Kukui however is just a waste of a Professor, Hala feels like he would make for a better Professor character than Kukui.
Untiered but mentioning Bianca since she's technically on the path to becoming a Pokemon Professor in B2W2, I do hope we get a game where she is a Pokemon Professor because I feel like she could be a better iteration of Elm, she's naive like he is although thanks to Gen 5 her personality is very well fleshed out and we know she's a competent battler.