I would like to answer my own question, since I just returned from Florida on CRJ900 for the first time. On the previous leg to Florida flew on ERJ 175, so can compare these 2 planes (regular economy seats). Both on Delta (to be precise, Republic/ERJ175 and Endeavor Air/CRJ900).

I thought CRJ900 was much worse than ERJ175 and I will try to avoid this plane in the future if I can. Here are the reasons why for me:
1) CRJ-900 has small overhead bin space. So you have to check-in your normal sized carry-on roller luggage at the gate. And because many people have to do it it takes quite a bit of time for the check-in agent to process everyone. And when you exit the plane we had to wait in a long line of people right in the jetway for your bags. We waited around 10 minutes.
2) If you buy regular economy tickets (and I did not have Basic economy, so could choose my seats in advance) and happen to sit at the end of the plane it is very noisy. CRJ900 has the engines at the back and we were sitting in a 2nd row from last (row 19) and the noise and vibration at times were quite extreme at times. And the in the restroom that is all the way in the back it felt like you were in a rocket ship of sorts.
3) The whole plane felt kind of flimsy. I know this very subjective and some may find it silly. But ERJ175 felt like a solid, comfortable plane. Similar to A320 or B737 in terms of comfort, handling, etc.
4) Perhaps this was just my luck and maybe this does not happen every time, but we had a pretty rough landing. Almost felt like the plane was dropped on the runway.
5) On the plus side, the seats were quite comfortable and the leg room was pretty good.