So what's the best MMO where you're doing "whatever", and you're most likely to see other players filling the world doing their own different "whatevers"?
EVE is pretty good for this since you'll eventually be in Jita at some point to really let the "crowd" seep in, in rather uncomfortable ways. Likewise it's pretty good about having different areas having different types of content (people there for mining, farming NPCs, exploration, and/or PvP content).
RuneScape is pretty above average as well. Having a pretty small world, chocked full of content, and is very above average at keeping areas interesting to all levels (whether through quest chains that cycle you to areas above/below your level, or returning to grind a low level skill).
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