Everytime I've went, it's been with a park hopper. There are those who say that it's not worth it, but the last day of everytrip is a "highlights" trip, and we have to park hop if I wanted to ride one ride, my sisters another, etc. etc. etc.
Not to mention, if you go to epcot and the kids aren't into it, you then move on to another park... it's not a whole wasted day. I'm into the whole "breaks at the hotel thing", but I'm at disney, so I definitly don't want to spend a WHOLE day at the pool!