Westbrook is the better player and Rondo the better PG. The Thunder need a high scoring PG because 3/4ths of their roster doesn't score. It's a team full of role players with three all around players - Westy, KD and Harden. They had a fourth, Eric Maynor, who was the best backup PG in the league, but he's gone for the season with a wrecked knee.
So Westbrook needs to hoist 20 shots per game, which he does quite willingly. The guy puts up great production, 24/5.5/5, and the TOs are a result of him playing high octane, out of control. He doesn't run a team like a traditional PG, but OKC is one of the top three offensive teams in the league, so he must be doing something right.
Westy has improved his jumper since entering the league, Rondo has not. Westbrook is the better player right now, and I'd take him even with him to earn more money in the future.