This is a tough question. Although he was drafted high, coming in to the NBA, it appeared that Harris had no clue. This is probably at least partially due to Avery Johnson and the demands of the position.
I'm not positive on this, but I think Harris has improved greatly on his outside shooting. Last year and this year he appears to have figured it out (obviously).
I think Rondo had better instincts early compared to Harris, but just a different skill set.
So I'm undecided. I'd be happy with either, but I'll pick Rondo just because he is the perfect fit for this team.
What I'm really excited about, though, is that these guys are both in the same division. Assuming they continue to improve and stick with their teams, this should be a great matchup for years to come.