I like Asylum and Origins the most. Origins has the best combat and I think the character designs in it are better too (I hate the bulky, blocky designs in the RS games). That's a controversial takes with Arkham fans though lol. City is good, ppl really hate the last act and it does feel a little weak but I fukked with it. Knight is STILL a gorgeous looking game but the whole experience feels really watered down.
Part of the magic with Asylum (and to a lesser extent Origins) is theyre really focused experiences. They don't try to do too much and really lock in a specific tone/atmosphere. Knight and City are both kinda all over the place in that regard.