Looking at player densities where I play, East Continent is pretty good but that's about it. Beluaterra is pretty fun to be in right now but the south is completely unplayable - only the northern two thirds allow for a relatively balanced game and this has skewed player densities massively. Dwilight has poor player densities made worse by a disproportionate number residing in Luria Nova. The Far East is generally good apart from two pocket realms which have pretty much 1:1 noble to region ratios. I don't know about other continents.
But it does seem to me that the best ratio, game-play wise, is a ratio of 3 nobles to a region. However, there aren't any realms (other than one region realms) which have anywhere near that ratio.
Funny you should mention that. The two realms closest to 3 nobles per region, Barca and Asylon, were both destroyed by the monsters. Kind of counter-intuitive if you think about it.
