Last year we went in both April and October and I enjoyed both of them.
April - We went from 4/28-5/2. I picked the last week to avoid the spring break crowds. The weather was sunny and beautiful. Shorts and tshirts all day/night. Wore a light jacket one morning at early EMHs. We swam each day. Crowds were light, probably a 4-5 each day. Unfortunately there was no Pirate and Princess parties the 5 days we were there. I would have liked to attend the party.
October - We went the 3rd week from 10/19-25. We avoided the week with columbus day, again to avoid crowds. The weather was great, shorts and tshirts, a light jacket one morning and one night. We went to
MNSSHP on 2 nights and loved all the halloween decorations at MK. It did rain 1.5 days. Crowds were manageable, about a 5 level.