Well, given the title, I have to comment: A DC9 is always better than a one class CRJ!

But to your real issue within the post:

The CRJ900 does have FC (12 seats), but don't bother trying to get a roll aboard in the overhead bin. You will still gate check it with that aircraft. Headroom is still tight (I'm 6'4"). FC is fine, service can be spotty and don't expect a meal.

The ERJ175 also has FC (12 seats) and full sized bins for roll aboards (get there early, they fill quickly). It also has headroom, at least 6'6". FC is fine, service can be spotty and don't expect a meal.

The 319 and 320 can speak for themsleves.

Lastly, any of the above equipment is probably better than the DC9, but not by much. Personally, I would avoid the CO 737s as they have so few FC seats, upgrading, even as a platinum is hit and miss.