awesome, i can provide a good answer to this, i have played both games very thoroughly.
Runescape is better than WoW for many reasons, the ability to log off it such a unknown necessity in MMO's and if there is one thing i hate on WoW, is the dependency that other players are going to have on you, so you basically cannot log off until you are 100% free.
The fact you can be what ever "class" you want to be is alot more fun. don't feel like useing runes today? no prob! rip out the sword or bow, the skills are so much more fun to level, and can be bought out with skillful money management using them.
Repetitive game play in WoW can get really annoying, always the same system to play, not much change unless an update or expansion is released. Runescape gets updates so commonly, and even builds on the experience with improvements on older tech
I hate WoW for one reason... unbalanced play! the characters are so dependent on armor, stats, and expensive things, and some classes can't handle another, and destroy the next is so frustrating, as Runescape is just a matter of saying "wow! this guy have 99 strength, no wonder he beat me!" while WoW you just go "Warlocks are not fair!!! why do they crit so much!"
the difference is really obvious when you play both games and dissect them both... Runescape is overall alot better, and can have alot more added to my list for why it is better.
~Cookaloo
This basically sums it up ^