Honestly, it varies as to what ride has the longest wait time. All the rides suggested above do get crowded. BUT... if you have a smartphone, I suggest you download the My Disney Experience app. It will give you live wait times and help you out with a bunch of other things such as looking for the nearest restroom or ordering food from the nearest spot to eat.
Toy Story Mania has the longest wait, but Haunted Mansion has a starting room that is probably the most claustrophobic.
The seven dwarfs mine train.
When we were there the longest wait was for Space Mountain
Right now it's the seven dwarves mine train. I would recommend getting in line as the nightly fireworks start if you don't want to wait more than 10 minutes to get on.
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