Here's how it seems to work: EVERYPONY wants to cuddle Fluttershy, fuck Rarity (oh c'mon, she's like the pony version of Jessica Rabbit; anything straight with a y-chromosome wants that), party with Pinkie, even if she is kind of annoying, and...anyone else know the rest?
well, if you want to get really anal about it, Danny from G1 was the original brony. Hell, he was a brony before that was a (good) thing. Plus, everyone who wants to fuck Rarity, probably also wants to fuck Roseluck.
I didn't even know that this show existed until I found some of the characters on Rule34, and saw the first season on YouTube; I was going to watch the first 5 episodes and see if it was worth checking out but I only had to watch the first two.
for me it was tales that got me hooked,eversince i first came across the the My little pony tales episode "The Slumber party" on Youtube a few years ago,then i started watching all the My little pony tales episodes,then i watched rescue from midnight castle and the original series,then G3 and not long after FIM came out i was watching that too lol.