Arkham City. Knight is good, but has too much (sometimes ridiculously difficult) emphasis on Batmobile missions.

My favourite, which is not on your list is still Asylum.

Arkham GOTY is the same as the original + DLC. Never bothered with either.

Thanks

The City game is the best of the lot, but the first one walks you through the mechanics that evolve throughout all the games and can feel a little basic if you play it after the sequels. 

I'd say the story in Knight tops the story in City, but both are equally far fetched and stretched out (given the playtime on these games is between 20 and 30 hours). 

Still, I think they're all worth playing.