I've been on 2 Stand Ups. 
Riddlers @ SFMM 
Vortex @ Great America 
Out of those Two, Riddlers is better by far. 
It's smooth, forceful, has a little airtime and is definitely rerideable. 
Vortex just needs a good retracking because it could be a really good ride. 
But right now, Its the roughest ride in Great America. 
I'll get to ride Mantis this summer, So I'll see how that is.