In my opinion they're both amazing but OSRS has a more toxic community from what I've seen. Because I'm so busy irl I tend to play RS3 as a more laid back version. I'm also maxed on RS3 but I get to relax and AFK skill mostly. I do like both but I do prefer RS3.
OSRS for sure because maybe it provides me a sense of nostalgia of when life was easy. Not really a fan of the new graphics and the combat system which made OSRS pretty fun.
I'm still torn between the two myself, I'm a sucker for updated visuals but if the core gameplay has bee dropped in terms of quality I can't say i'm too interested