I don't like preachiness.
What I do like is that an author teaches me something, beyond telling me a good story, without being preachy. I mean, if after reading a story, I get a sense of why being a vegetarian is a good thing, so be it. I'll be glad to listen. But don't whack me in the head with a 2x4. Also, if every good character is a certain way (vegetarian, animal-lover, etc.), and every bad character is another way, IMHO, it's lazy writing, stereotypes, flat characterization. Your characters should be human first, and not just objects that fit well into predefined boxes. For example, in a great political satire, not all Republicans are selfish snobs, and not all Democrats are whiny liberals. When you shy away from these stereotypes, that's when your characters and story become real and interesting.