I said I have no preference in either, but after thinking some more, that might not be entirely true. I think I'm a little more apt to be critical of fanfic written in first person—but just a little. It never stops me from reading it. (I think a story where the narration is off will have dialogue that's off, too. A mild case of either or both won't prevent me finishing; a bad case of either can! I still tend to persevere once I've really started, however, which I think I need to cure: some things aren't worth finishing. That's true in published fiction, too.)

I wrote an SG-1 story in first-person ("Charades", if anyone's curious; Sam narrates) partly to challenge myself as a writer, because while I read either, I very much prefer to write third person. It was only after I proudly posted the story, reasonably happy with the results, that I found out at least one of my friends makes a point of not reading first person fic, especially not when it's Sam! I don't know how many readers that might have cost me. I might not have tried first person in that one if I'd known.

Then again, maybe I should just write what interests me and not worry too much about readership. That's what I do in academia! :-)