Best use of the 50-seat CRJ's is for competitive/market share reasons, (ie. Frequency).
Always own them, it's real tough to make money when you lease them.
I really do like them them, for several reasons. They open the door for later, larger CRJ's, and can be wildly profitable, even at higher fuel levels, with high utilization. They should be an addition to your fleet, but never the backbone of it. They are a great, cheap way to open new markets, while the RI builds. Then you can replace them with larger aircraft.