Fanart because that's usually what I look up. I still favorite good pictures of OCs, but since they're not usually what I'm looking for, I don't tend to find + favorite as many.
I'm more likely to look at fanart, honestly, because I am familiar with those characters. I like OCs, but I've never found myself too obsessed over someone else's.
I tend to favorite both about equally. As long as the art work appeals to me in some way, I will favorite it. I tend to favorite Fan art more if I recognize the characters in it though.
I used to do lots of fan art. Not so much anymore. Once in a while.
For favorites, I won't do it because I like the character, I do it because I like the art. So it doesn't really matter. I have fanart from stuff I've never seen, or in some cases heard of, in my collections because I like the picture. Same for original work.
I'm way more concerned in the actual work of art than the contents.
Personally, I favorite originals more often because I like seeing what other artist's minds are like. However, sometimes I favorite fanart because either I'm in love with the character(s) or the artist did an amazing job.
Just curious.