both are good.
Cruises are good especially if your kids like kids club type things, arranged activities etc. There is still plenty of family time and relaxing or doing things together - but you also get a break while they are stimulated doing fun things.
On a resort/beach ... its super relaxing as its just you guys. There is a bit less to do at times, but it totally depends on the type of holiday you want - sometimes that is exactly what you are looking for.
with a cruise I found that the kids met other people more, and made friends a bit easier (and us too) because you are all there at the same time. With a resort, people are coming and going all the time, so often the person you meet and find friendly is leaving the next day.
Anyway - both are awesome (but I am in holiday mood so anything is fantastic at the moment (