They're all growing on me, but so far Rainbow Dash. Who's yours?
I think—especially for a kid's cartoon—all the characters are actually complex and that's why the show is so interesting to adults. They wanted to make a show that was interesting enough for parents to watch with their kids, and did such a good job that now adults are fans in their own right. That has to be cool for the creators of the show to see.
I have a preference to Applejack, since I am currently residing in the southern US and the people here are very much like her. But Rainbow Dash's personality is like mine, so I also like her. But I also like them all, it is hard to choose, each one has something extremely likeable about them.
I know Lauren Faust, while not expecting it to be so big amoung young men my age, has embraced it. She has so many cultural references in the show, and especially season 2, always has something for the bronies. It's kind of cool because she actually goes online and talks with the bronies and defends them if any jerk says something about them.
You have those weird bronies that um, preform unspeakable acts, but I stay clear of them. Most of us are, relatively, sane.