OKay our last 2 trips have been in Feb & April. We went April 2002 and the February 2003.
February: We went the 2nd week. The morning and night time temps were chilly-- long pants and jackets. During the day it would reach the upper 60's-- I think the lower 70's once or twice. The biggest problem was dressing for the day. With the sun, the afternoons could get a bit warm-- but the we stayed for Fantasmic & Illuminations-- which was really chilly. So dressing for the day was a bit of a trick. The crowds were pretty low everywhere except MK. Even there though-- our longest wait was about 20 minutes. We didn't use FP's anywhere because the other park waits were only in the 10 minute range. We were able to walk into a few decent restuarants w/o a PS as well for lunch. We got to swim 2 afternoons--but had to "run" right back to the room. We only had rain the day we arrived and the day we were leaving. Oh and one really brief afternoon shower while we were at Epcot.
April: We went the 1st week. This was a year were Easter was March 31st (or April 1st). Anyhow, we arrived 6 days after Easter. The weather was in the low 90's everyday. Which made for really hot, hot, hot days. It only rained one day here as well, it lasted for a few hours. It was a bit buggy on this trip. In got "all bit up" one night. The crowds were average I'd say. MK was totally mobbed. The other parks were managable. We fast passed a few things and waited on the average 20-25 minutes for other things. We only had counter service in the parks this trip as waits w/o PS were going 60-90+ minutes. (DH doesn't like the obligation of a PS--that's a whole other thread though).
If possible I'd like to go smack dab in the middle of these 2 times. That would be a great combo. I'd like the weather to be a bit nicer than February but not as hot as April. The crowds were great in February though. Of course the park hours were lower though too.