Hey again Keila,
Welcome back to planDisney! I'm so glad that we here at planDisney get the opportunity to help you plan your best trip ever to the Most Magical Place on Earth.
Over the past few years, the question of which ride to book first for your
Lightning Lane Multi Pass has gotten to be quite tricky to choose from. As a disclaimer up front, it will largely depend on your own ride preferences and I would also take into account if there might be some of these attractions that you've never experienced before. If so, then I would definitely prioritize those.
However, with that out of the way, here is how I typically prioritize that first Lightning Lane Multi Pass booking for the day. Ultimately, it's going to be between
Frozen Ever After,
Remy's Ratatouille Adventure, or
Test Track.
All three of these attractions tend to have longer queues for a majority of the day. When visiting with my family - we have 8- and 5-year old kiddos - we almost always opt to book Remy's Ratatouille Adventure first. The reason relates to my other answer to you: we love to get crêpes before or after we ride! We then will typically try to book a return time for Frozen Ever After as soon as we can after that.
The only reason we haven't prioritized Test Track as much in the past is because our younger kiddo can't ride it yet. Additionally, my family and I more typically visit the Disneyland Resort in California and there is an attraction there that is quite similar to Test Track, but there is nothing like Remy's Ratatouille Adventure or Frozen Ever After, so we like to experience those when we visit the Walt Disney World Resort. However, if I was on a trip with friends then I do actually think Test Track would be my first priority to book.
Thanks again for stopping by planDisney and I hope you have a wonderful time on your upcoming visit to the Most Magical Place on Earth!
Have a Magical Day,
Greg