Hmm... My favorite writers so far are probably Berka Zerka, Endmaster and Seth, but I wouldn't say I've actually read enough of the really good games on the site to give a well-informed opinion.
My favorite genres are probably Fantasy and Mystery/Puzzle. I'd say whether I prefer game aspect or story aspect depends entirely on the game. Games like Necromancer have such a strong, interesting story that I'd hardly consider it a game at all, just a book with several different endings. On the other hand, you get some really good puzzle games like Game of Life and Death that're genuinely difficult to solve, and games like Dungeon Stompage where the scripting is so unbelievably complex it makes the game aspect even more fun than the story. ^_^
I'd say my favorite story over all so far would be Eternal, but I might be biased 'cos I've only just finished. Other favorites include Death Song, Dead Man Walking, Snow, Avery M; Dead Man's Journal ('Cos it's so different) And of course... Kill Aman's Mustache!
... And now I want to read Haunted again. It must've been awesome 'cos I rated it really well, but I swear I can't remember it for the life of me.