We have been fortunate to be at Disneyworld the last several years over spring break. We usually always go the same week that you are going. Magic Kingdom is always the most crowded, then Epcot, MGM and AK are about the same, tied for 3rd place.
Some tips, if you are staying onsite, the EMH is a must. Last year we stayed onsite for the first time, and didn't take advantage of this, and boy, were we sorry. I know it's early, but, let me tell you, last year it was Easter week as well as Spring Break, and the MK was unruly!
Also, I usually go with the idea that I will not see and do everything on every trip, which eliminates us from running ragged.
So, expect some crowds especially at the MK. It shouldn't be that bad if you have an early start. If you are staying offsite, check to see when the EMH are and go to the park that doesn't offer it, to avoid being at the park the same day as onsite guests.
Have fun! We keep doing it every year so it can't be that bad!