Snips and Snails aren't the most flattering way to show what the crew thinks of young boys, but they're minor characters at most.
Diamond Tiara was usually the instigator for some of the show's worst episodes, but there was a cuteness to her at least.
Starlight Glimmer is odd because half her episodes are trash while the other half are fantastic, there's no middle ground with her.
Angel Bunny, while an abrasive brat at times, is just a lil' rabbit who doesn't know much better.
The worst thing you can do is introduce a character and just expect the audience to like him or her for no reason. If this were a while ago I would've said Big Macintosh due to his lack of personality, but then Hard to Say Anything came along and, y'know, gave him a personality. : )