What is The Best Minecraft Modpack?

Well that purely depends on what you want out of the modpack. Some people want modpacks that simply have a lot of mods in it, for that I recommend Resonant Rise 4 and select as many mods as you want.

You may want to follow a quest book, for that I recommend Project Ozone 2: Reloaded. Alternatively you might want a quest book based modpack that isn't easy, for that try Forever Stranded or Agrarian Skies 2 which is a quest based Sky block modpack.

At the end of the day, it all depends on what you want out of it. If you just want a bunch of mods to mess around with then something like Resonant Rise is ideal. But you may want to follow quests or have a challenge which is where quest book modpacks are good, they're built around you following the quests.