They're both amazing looking Stand Up coasters, however I think that Riddler's Revenge looks a little bit better.
First of all, it has more inversions, and inversions are pretty much what Stand Up coasters are made for. It's also faster than Chang, and taller than Chang, be it only a little bit.
However, I think I prefer Chang's colour scheme better. It stands out more and I like where it's situated better.
I think overall they're the two best standup coasters in the world and they both deserve some kind of credit though Riddler's Revenge looks better by a little.