We did the 4-land/3-sea last year(6-01). We went through disney and used their package. It was very convenient because we didn't have to worry about planning too much. I'm sure it is cheaper to set it up yourself.
We had been to WDW the year (6-02) before for 5 days and had a great time. Since it was the 1st time, we tried to do as much as possible. We felt like we missed somethings, so we decided to have a second round. Unfortunately, it rained alot on the 2nd trip. We did our best to get around, but we felt very drained trying to get out in the limited good weather. It wasn't alot and we were out in the rain quite a bit.
In hindsight, What we paid for the land and sea we could have done the 7-day for a little more or even the 3-land/4-sea. We had never cruised before and were not sure how we would like it. I have a tendency to get motion sickness and I didn't want to spend the whole time sick. I only was sick the 1st night-but there was a big storm.
I think your decision might be partly based on if you've been to WDW before. We're going back for more of the cruise. 3-days was definitely not enough. We only are doing the 3-day again because of the expense. Maybe next time!
Good luck on your decision-but it's disney so you can not go wrong.