IMHO, I guess it would depend on how long you plan to visit WDW or cruise with DCL. Personally enjoy the extra attention I receive from the cast members when I'm on a cruise.
I've done both and found them both enjoyable in different ways, but WDW is my favorite.
DCL is more relaxing, with the feeling of being pampered. I imagine one main reason for its popularity (besides the characters) is that the kids clubs give parents the chance to be off-duty for a while. There is no equivalent to DCL's kids clubs at WDW.
WDW is more high-energy fun and action: no attraction on a ship can compare to Disney World's rides, parades and fireworks displays (the DCL fireworks are tiny in comparison). You trade in the relaxation and pampering of DCL for an infinitely greater variety of attractions. The table service food at WDW is better than what you'd get on a DCL cruise, and your room will be bigger.
If your group primarily wants to kick back and relax, with a little fun thrown in, they should cruise. If they're looking primarily for fun, with a little relaxation thrown in, they should go to Disney World.
With your age group, I think they may like the cruise better. Are they interested in the craziness of the theme parks, or relaxation of a cruise? The biggest consideration would be the cost, Disney cruises are expensive!