Torn between Fireworks Festival (I loved playing with friends everyday, the festivals made them special) and Toy Day. I also like the solstices, they're really cool too.
I honestly loved the Fireworks Festivals. The music is really nice, plus it's just relaxing and fun to be with your friends and see fireworks at the same time. I also like how they didn't plan it to be on the 4th of July since most people will be out with their families instead.
Toy Day is my favorite because it isn't super annoying trying to get all of the items. Halloween is fun, but after a while it gets boring looking for Jack repeatedly and hoping that he gives you creepy stuff instead of spooky stuff since there are a limited number of lollipops. Festivale is cool, but when I was trying to collect the entire Pave set, I wanted to shoot Pave after watching him dance for the 20th time. New Years and Fireworks look pretty, but there is nothing to do except talk to Isabelle and Redd.