I've done both, and I don't remember any difference as far as crowds in the the parks are concerned. In May you have the Food and Wine Festival in Epcot, in October you have Mickey's Not So Scary Halloween Party in MK. Both are cool. This is the last year for Minnie, rumor has it that next year it will be replaced with a Princess themed half marathon. Robert's source said it might be in March. HTH!