What MMO would someone the biggest "pay 2 win" advantage in?

An academic question. I don't play MMOs, I just started a job with insane hours, and if I were to waste money on a game, it'd probably be cosmetic items in DotA 2 or LoL.

Still, if someone wanted to buy their way to a power position in an MMO, what game would that be? I only know of the mainstream titles, and all of them seem to have mostly 'pay for cosmetic items' systems.

This thought entered my head while watching Dan play WoW the other day, and it won't let go. Unfortunately, I'm no where near qualified to answer my own question.

Probably WOW its still the biggest MMO around and the legendary weapon drops are incredibly low.

Probably one of those super sleezy korean MMOs.

You can't pay money for those though unless you do so outside the system.

Most bad MMOs will let you buy power, and in a lot of older free to play experiments you have to pay for certain character classes or races in the case of DnDO.