I think one big difference between the two is ribbons seem to be more of a specialized feeder. They can be trained to eat different prey items but scenting of prey seems to be necessary under most circumstances.
The other difference seem to be attitude. Meaning ribbons are more jumpy and don't seem to calm down the way most other garters do.
These are just my observations with the one ribbon(Gulf Coast ribbon- Thamnophis proximus orarius) I keep.
I for one will be watching this thread for some of the other posts.
I feel I have so much more I need to know about these wonderful garter snakes. I also hope to breed my big girl (Shyblue) someday.