Overrated: Fluttershy, Luna, Trixie
Underrated: Applejack, Celestia, Spike, Apple Bloom (Kind of)
I'm not really a fan of Trixie or Luna, but I'm not calling them bad.
I don't know how to answer that question since I never thought about it. It actually does remind how the day before Valentine's Day, a brony confessed that he liked me with a drawing of Rainbow Dash.
I'll re-watch both season, except for the series openers. I've already seen them 3 times. I'll make fan projects. Perhaps I can get some other people to become pegasisters while I'm at it.
"Best Pony" arguments are pathetic. Everyone has their favorites. Mine is Twilight Sparkle because when the others are fighting, she brings peace to the Mane 6.
I can see either sides of the argument. For someone who doesn't like the show, for example, seeing it all over the Internet, it can come to a reasonable person impression that it is overrated.
I re-watched the second episode last night and it reminded me how Pinkie Pie's voice has changed to me. It has started to sound deeper overtime, at least in my ears.
I'm not a Sonic fan, but I saw a few episodes of that show in Japanese for the fun of it about 2 years ago because I was bored and wanted something to do. I remember thinking the first episode wasn't bad, but I couldn't watch the rest because it just didn't interest me. (Especially that kid being all over the place.)
I have thought about what would happen if humans appeared, just like how there were people in the old My Little Pony cartoons. I think the show would go downhill if people were introduced.