I assume you just want to experience a bunch of mods all at the same time, and learn about them that way?
In that case, I'd recommend either
A) Agrarian Skies 2 (modded sky block, with lots of quests)
B) FTB Infinity (Lots of mods in a normal world; no quests, though)
If your goal is simply (more or less) to learn about mods, your best bet would be to choose a pack which seems interesting, and follow along with a youtube LP series of that pack. Then if you want to learn more about a certain mod, do further research.