I have little interest in sterling characters who fight for the right, without a blemish or a flaw. That’s a good thing actually, since no one else does either. My only exception is Kimball Kinnison (of the Lensman series). That’s him overhead, walking with his buddies Tregonsee and Worsel.
I have no interest in literary characters who live their little lives and make novels out of the trivialities of existence. Here is a test; if a book seems to only have readers because it is required in college literature classes, maybe you should just go read some science fiction.
I like people — and characters — who do their job and a little more; who don’t think that the sun rises and sets in themselves, but who are also not passively afraid to assert themselves.
I don’t like villains who are deeply and intractably evil. I make use of such characters if I need them, but I keep them off stage. They are boring, seen up close.
I like my villains to be like my other people, rational and a little bigger than life, but affected by a flaw of character or aligned to the wrong side. They are usually selfish, but good heroes always have a bit of selfishness as well.
An interesting hero is necessary; an interesting villain is a nice bonus.
I don’t expect other authors to have similar taste, and some of my favorite books have characters I would not have chosen to write. Genly Ai comes to mind. If you don’t recognize him, he is the character through which we experience Ursula le Guin’s the Left Hand of Darkness. It is a fine book, and he does the job her story requires of him, but he is a bit of a cypher. I like Sparrowhawk better, and that is probably a big part of why I like A Wizard of Earthsea better.
And then there’s Alvin (or any other character that Arthur C. Clarke ever wrote). The City and the Stars, in either of its incarnations, (See 332. and 333.) is a mind expanding tour of the universe, but its protagonist is dull, dull, dull.
Zelazny’s characters are universally smart assed, universally delightful, and hard to tell apart.
Heinlein’s characters are all Heinlein.