Hi Denise. Let me start off by saying a lot of people may not agree with my suggestion! My family loves to visit our second "Home" during the hot months of June and July. Yes, it's busy and crowded. Yes, it's hot. Yes, we love to be in the mix! But there is a secret to our madness - early mornings. We make sure we are at the Parks at opening and we usually leave out by noon. We then retreat to the Resort for swimming, lunch and/or nap (especially with the little ones). If you are really adventurous, then you could head back to the Parks to enjoy the evening festivities. This is usually our touring plan when we are on vacation.
Now, if you are the total opposite from me, then I would suggest the month of May. It is usually not too hot or crowded. Actually, the weather was perfect when we visited in May 2009. And to be quite honest, there really isn't a bad time to visit Walt Disney World if you know how to tour the Parks. If you have additional questions, please ask away! We are here for you!
I hope you have a magical day!
Ca'Sandra