Having ridden both attractions, I have done my own comparison. Test Track has all of the show building elements (dark ride) first, and saves the "race" for last. I found myself getting a bit tired of the dark ride elements and then wishing that there was more of the outside race portion of the ride. RCR seems to have the best balance of the show building scenes and outside track scenes (plus the rock work is breathtaking - possibly Disney's best to date).
What say you?