Well, both games vary in many many ways. What i like about runescape is that you can be a archer, mage, or attack with melee and switch when ever you like. And in wow you can't but, you kind of need that aspect of the game to make it fun. Another thing i really enjoy in wow is that its combat based, some people may say runescape is combat based but, in my opinion i think jagex slowly changed that over time. Personally, i think runescape turned into a monopoly, since theirs some people that still adore the game and other that hate it, but they see a great opportunity.
Anyhow for my final decision i would definitely pick World Of Warcraft over runescape.