World of warcraft, hands down.
I don't really play either at the moment (rs or WoW) but played WoW for around 6 months recently. The only draw back is the addictiveness. I spent toooo much time on it!
WoW offers AMAZING pvp, quests worth reading, so many diffrent equipment types/levels. Every account is unique, even the twinks (pures) are different.
Once you hit level 40, your character pretty much becomes two when you dualspec. For example, I played a healing priest to level 40 but now I can both DPS and heal on him, meaning that I can quest but also instance in seconds.