It's all about a balance between the two but I'd say polish is more important. This is especially true if your game has PvP which will keep people entertained for quite a while on its own. So long as the majority of players have something to do for a few months you should have no trouble getting out some additional content in time. If the game isn't polished though people will leave within the first few weeks or months of the game and never give you the opportunity to patch it.

Just look at WoW, they went for the polish first content second and it's worked out great for them.