Hi, Christina! We have something in common! I'm totally addicted to the panel, too, and can't seem to start my day until I come here and see what we're all talking about!
Okay, you don't say whether or not you have children, and you don't mention if you're an early bird or a night owl. We've got a little bit of everything in my family!
I prefer the earlier dining times. I often find that the restaurants are not very busy early on, as many people are still enjoying their theme park time. With a five year old, while I know she can stay up until past nine at night, I can't rely on her to be pleasant that late in the evening, so it's easier to take an earlier reservation and know she'll be socially acceptable to sit in a restaurant. I am also an early bird. I like to get to the theme parks by rope drop in the morning, and if I am just sitting down to dinner at after nine, I am likely to fall asleep in my salad, and be totally ticked off the next morning that I'm too tired to get out the door as early as I'd like.
If my husband were answering this question, he would totally tell you the later time. He likes to make the most of his day in the parks - once he gets there - and he is definitely a night owl. Nine o'clock for him is just about lunch time, and he'd be happy as a clam to sleep in until later the next morning.
Go with what will work better for the majority of your family. Keep in mind, you may not be finished an after nine o'clock dinner until nearly 11!
Have a great vacation!