I don't know. I wouldn't have given it to Aaron Brooks, mostly because I think players are supposed to experience great strides in their game between the first and second years. Frequently, I don't necessarily attribute it to a growth in their actual skill set. While he and Westbrook and Durant undoubtedly improved, I think their better stats are as much a function of increased minutes or familiarity with the league over a full season than they are of improvement. For that reason, I'd be more inclined to look at guys like Gerald Wallace, or Andrew Bogut, or Josh Smith.
Feel free to disagree with me - it's more of a gut instinct than a researched opinion, and there's no denying that Aaron had a very good season (even if it was on a team with no other legit scoring threat for much of the year).