I voted graphics. How a game looks is the second impression any new player gets (the first being download/registration/installation process).
And let's face it, we need more players.
Certainly, people will argue now, "quality vs. quantity", "we need only the "right" kind of players" (whatever that is, the opinions obviously differ greatly at this point. In my humble opinion, the evolution of the player base is a natural process anyway. You can try to direct it a bit but you can't force it. )
But.
These days, all commercial games, even those as old as Morrowind (2002) with the right mods have shinier graphics than PS (probably also most free games, but I lack experience there). People are spoiled. Prettier textures, more models and animations to look at, maps to explore and clothes to try might keep a lot of players at it until they get to appreciate the ingame community and roleplay. I know from my own experience as a newbie that this might take at least a few weeks of lonely stumbling around.
And more players will mean more chance for casual and organized roleplay, yes, also more levelling, cities looking more alive, more ideas, more potential bug reporters, bug fixers, tester, contributors, GMs and even full devs. More everything.