Okay, here are the differences, probably as you'll notice them.
Amenities are the selling point - Rock Climbing, Ice Skating, Roller Blading, Surfing, et al.
Food is more of a buffet style lower quality (using CCL as a reference point)
RCI implements a 1 am. curfew for underage cruisers
RCI's teen facilities are usually about the same as CCL's if not better.
RCI's nightlife for teens last from around 9 or 10 pm to 1 am; no exceptions.
RCI's staff are usually there to improve your experience - unless you're dealing with rent-a-cops.
Fun is the selling point - a lot of deck activities and family activities
Nightlife is very strong - expect to see people up and about at 2 or 3 in the morning
Teens are not restricted by a curfew
The teen directors are very open to ingenuity - feel free to get a group of friends and do a "Greek" night and all where Togas to Club O2
Food is typically above and beyond the quality of RCI - from the Lido Buffet to the dining room.
CCL staff are very trained on the fun experience - they are usually fun, casual, and very open.
I would not hesitate to take either line (and I have taken both in the past), but if CCL fits better for your schedules, by all means, you will have just as much fun on the cruise. I would not hesitate to take it. Also to keep in mind that you'll probably save a few bucks if you take CCL over RCI.