Warner Bros. has released a trailer showing the visual difference between Batman: Arkham Asylum and Batman: Arkham City on the PS3 and the PS4. Watch the trailer and decide for yourself what looks better. To me, I think the backgrounds are improved, but the character models tend to look better on PS3 in several cases. Pay close attention to Joker especially.
It becomes increasingly clear, in my eyes at least, why this game was delayed by three months.