I like unusual characters with realistic bodily proportions the most. I'm not a fan of extreme fetishes like macro or inflation, but I do like to see a good range of different body types from chubby through to skinny, or tall to short. I tend to prefer 'real' animals, but the odder the better - insects are a favourite. I don't mind an occasional sergal or protogen, and recognisable mythical beasts like dragons and gryphons are fine, but I don't like random hybrids and most other 'original species' just look silly to me.
That being said, a good artist can make anything look appealing, even boring old foxes and dragons. It's all about how much character you can get into your... er... characters. I like to look at just the picture and immediately know what that character is like as a person.
On the other hand, I don't think I'm remotely typical of the fandom!