Online as in MMORPG or just multiplayer?
Anyway, I don't see it that way. The best RPG's are the singleplayer ones (Divine Divinity, Beyond Divinity, Morrowind, Lands of Lore,...). Baldur's Gate is of course also a masterpiece and that game you can play in multiplayer, but as far as I'm concerned that's never as much fun as playing it in singleplayer with the party-interaction.

I am in blood
Stepp'd in so far, that, should I wade no more,
Returning were as tedious as go o'er.