Neither. The longer I play Elder Scrolls games the more I'm interested in playing characters who change. Playing characters who conform to Manichaean concepts of "good" and "evil" is less and less interesting to me. I have little patience for either/or thinking. I play to find out how my characters will be influenced by events. I play to experience their story, and a big part of that story is how a character changes. An unchanging character in any narrative is an uninteresting character. And that goes for video games as well.
There is no law that states characters cannot have both fixed *and* mutable aspects - just as many real people apparently will, in fact. This is the case, for instance, with my Paladin. Yes, she is "good", in a number of core ways.* Otherwise though, she has been through rather a lot of changes, including being more open- or closed-minded at times, going on a bit of a bender just recently, looking at people and the world in general in different ways (due to confrontations, realisations, musings, etc.), reacting differently to repeated situations (according to context, mood, history, and more), and certainly (on occasion) questioning the very virtues she clings to so fiercely in the face of all the evil and apathy in all the worlds.
I've found this provides quite enough rich roleplaying fodder. YMMV, naturally.
* And there are reasons, too, for this. Including childhood experiences, a chance encounter with what was to be a mentor of sorts, and so forth...
Oh, and to answer the OP: I tend to play either "good" or "neutral" characters, though "evil" is not necessarily off the menu. Lately, I've been having a lot of Paladin time. "Rangers" have also featured strongly.