We spent last week there and got back late last night. We usually go in the fall and I think we will stick to that plan in the future. We found it quite cool. Of course I shouldn't complain with the crappy weather out there tonight! LOL! It was warm from about 1 -5.
It was quite busy and required alot of careful planning. We found If you were at the park when it opened and used fast passes carefully, waits were manageable. Afternoons were incredibly crowded, but tended to die down in the evenings.
The one thing I found interesting at this time of year, was that although the parks were very busy, fast passes were available longer than in the fall and the resturants never seemed crowded and we had no trouble getting 7 in on standby. We wondered if maybe at March Break there was more visitors that maybe didn't understand the fast pass thing or know how to make a reservation and fall you have all the Disney fans for Food and Wine and
MNSSHP. Don't know? I found it interesting that people would get in a 40 min wait line up, yet the fast passes being given out were for a return time in less then a half hour. Why would you wait in line for more time unless you had a fast pass for something else. Who knows?
We stayed at OKW and never found it crowded. It seemed no different then the fall.
There was a lot of high school groups and the first part of the week cheerleaders and dancers. We found them all to be very well behaved and respectable. I loved seeing all the marching bands before the parades. Or listening to the different choir presentations around the parks. That is something we don't see in the fall. The Garden festival at EPCOT was beautiful and worth seeing. However now I am bummed, because I want to see color and flowers and instead all I see is white!

Good luck with your planning! I'm sure you will have fun regardless of the time you choose. You just have to decide what you want in a holiday!