| It depends on what you seek. Without saying "for what", your question is akin to "what is the best TV show". It totally depends if you like sci-fi, cop shows, sitcoms...
If you want PvP action, tentatively Shadowbane I'd say. DAoC's PvP has too many issues to be considered best.
If you want PvE action, EQ remains so far the strongest contender. AC1 could have been the best contender, if stuff like macroing and the like had been fought since the beginning. As it is, it's dead and broken.
If you don't want hack-n-slash, A Tale in the Desert is probably the best. Specially since you can brew your beer now (only lambics, though). | 