They're all roughly the same, at a 3 or 4, with the exception of the CR7, which I've found to be in great shape.
The regional jets at all carriers get some rough treatment; lots and lots of cycles, lots and lots of passengers loading and unloading bags many times a day, compared to a 737 which would make, on average, longer stage length flights and have fewer bags stuffed into overheads throughout the day.
That's my experience, anyway. ExpressJet's ERJ's are in pretty sad shape, just from abuse. American Eagle has some similar examples.