Before. Makes the relaxation of the cruise amplified.
IMHO - I would suggest cruise afterwards. The cruise is soooo much better than the parks that you would be disappointed the otherwise. You won't regret it!
I generally say parks first & then cruise, but since you don't list who will be traveling with you I will add this additional thought. I have a 3.5 yo who loves WDW more than just about anything. If I were to take him to the parks and then try to confine him to a ship he would bug me to death for the cruise asking to go to the parks. If I were to take him on a cruise first he would love the cruise and would be delighted by getting to go to the parks as well. Unless you think this will be an issue, I say go to the parks and then spend time relaxing on the ship.
I have been trying to figure this out too. I wasn't sure if we should split it and go to WDW 2 days before and then two days after cruise.
We did a 4 day Dream cruise, followed by 4 days at the parks in June, 2012. I think we would have liked it better if we did it the other way around (still a fantastic time though) Although Disneyworld, Epcot, Universal were great, it was very HOT and very crowded, and not as relaxing as the cruise. Any time we were sweating in a long line at one of the parks, I kept thinking we should have done the cruise second....