I have a child with sensory issues and love Universal's child swap! I never have to give a reason why my 8 year old needs child swap - they're always fine with it. (Meanwhile, at Disney they don't let us use it if the child is a smidge over the height - even when he was 3! I asked about allowing it due to his sensory issues and was told that guest assistance passes would help him ride - not help the rest of the family ride).
The rooms do vary with noise, crowdness, and darkness. Despite his sensory issues, he actually does quite well in the FJ room. The MIB room is our favorite - light, not crowded, and not loud. Plus, you can watch people get on the ride. (Also, it's easy to use both single rider AND child swap for that ride due to where you enter child swap. Some rides wouldn't let us use both so just ask before you get on). I think RRR is one of the few child swap rooms we haven't used. There's a nice place to sit right outside the ride on the fake grass. Also, sometimes single rider is short enough that you can send one adult to do a ride while the other does a ride with the child. Hulk usually fits this when we are there. Hulk has a sign saying how long single rider line is too - not all rides have that. Storm Force is right next to it - it's like teacups though it seems like it's faster to me. (I can't even watch it due to dizziness - I send my husband on that one with our youngest while the oldest does single rider Hulk and I go with the middle child so she can do single rider Dr. Doom).