I've played both games to the endgame (can do Lucid & Will on MapleStory). I think MapleStory's endgame lacks the competitive part while RO provides WoE and PvP.
Both have its chore (instances and bosses dailies), but RO gives me more satisfaction with each WoE while MapleStory boss fights get more boring each time you do it.
btw I play Kinesis, I love torturing myself.