Personally, I enjoy riding Scream more than Riddler's because I enjoy the smoothness of Scream compared to Riddler's. Riddler's (especially the last element (I'm not sure what the technical term is)) is much rougher than Scream. In addition, the forces towards the end of the loop pull my whole body towards the ground, causing pain in my feet, legs, and my male parts (which is why I now always sit down on Riddler's, even if I need to be yelled at by the ride op).
I find both rides equally entertaining (perhaps Riddler's even a little more than Scream), but I prioritize my safety ahead of the excitement (though now, I've figured out that sitting down on the bike seat truly works wonders; it makes the whole ride painless).