Ok, is this a feature of mine I love, or in general? If it's me, I don't have one I love, but my favorite would be my eyes, although I'd like them better if they'd just pick a color and stick with it. They used to be blue, a gray-blue color... now... sigh, they wont pick. They look more green-ish now, but they are not a true green by any means. Plus, they feel the need to mix it up more by adding amber-ish color. Ugh, how annoying. Ok, so it's safe to say that it's the shape of my eyes I like best, not the color. And just to clarify, my eye shape is nothing special, it's just my best feature.
If it's not me we're taking about, then it's smiles! I love them, they are contagious! Everybody looks so much nicer with a smile. Enough said ;)