Not really sure how I feel about megas. I like the idea, but I think they were given to the wrong Pokémon. Like Blaziken, Garchomp, Tyranitar, Rayquaza and Salamence didn't need a mega to begin with.
And the Pokémon that got a mega and actually needed it like Glalie or Steelix aren't so great with it. Who here remembers Mega Steelix or Mega Audino? I didn't until now.
I'm glad that they stopped being a thing, although Dynamax is no better than it.
That said, my favorite one is probably Aggron, Mawile and Salamence's