Asylum and Knight are my favorites of the series. Ranking them is difficult because each has something that I love and appreciate. I've played through these games multiple times and very rarely have anything that I disliked. I'll probably do it again after I'm done with Kingdom Hearts.
Asylum (Best atmosphere) > Knight(Best open world/Worst boss fights) > City(kinda average compared to the rest, still a blast to play) >> Origins(Most glitches and crashes I've ever had to deal with in any Arkham game)
Asylum (Best atmosphere) > Knight(Best open world/Worst boss fights) > City(kinda average compared to the rest, still a blast to play) >> Origins(Most glitches and crashes I've ever had to deal with in any Arkham game)