MGM is our least favorite park. To us, if you've done it once, you've done it enough. Of course, we LOVE Rock N Roller Coaster and Tower of Terror. For us, it has become a half day park. If you've never been there before, I think you should plan for a day there. A lot of the opinions you will read here are from people who have been to WDW over and over. After you've been a couple times you start to stop going to the things that aren't your favorites. I think you need to look at a guide book and see what there is to offer at each park or even find someplace online. Then you will know what appeals to you. If you have little kids, you'll want to do Playhouse Disney. This is something that I've seen enough, but if my daughter wants to go, we'll go again. I think it is a small park, but a lot of what you are doing there are show type things. So, it will take time.
As far as Animal Kingdom goes I remember going for the first time in September. It was so hot. I remember that. I quit doing my hair, because it didn't make any difference. I remember thinking that I didn't even want to go to Animal Kingdom. I was going to skip it. We decided to head on over and just check it out for a couple hours. We ended up spending an entire day there. I don't remember being horrible hot. I just remember loving the atmosphere there. I loved the attention to detail. And, they have some fun shows that you don't want to miss.
My opinion, is that you should keep yourself open to be able to enjoy more than a morning if you so choose to do. And, more than half a day at MGM if you choose. If you get done with the parks earlier, then you have free time on your hands.
