I chose Dwilight, Beluaterra, and EI.
Dwilight because I <3 it way too much for my own good. Its vast, has unique geographical situations compared to other continents, vibrant history thats still affecting the present, more frequent turnover, religion that matters to characters, and has the one-noble-per-family rule. Its played by about half the playerbase, from my rough estimations, so that gives me an initial understanding that it has good player density. It also has a good record of player retention, in the past (though I still think a retention study should be done before choosing an island). I do think Dwilight should have increased rogue spawn rates though, to make up for its increased size.
Beluaterra is still dealing with the ramifications of its changed geography, has good character density, more frequent turnover, and a vibrant history thats still affecting the present. It also has a good record of player retention, in the past.
EI and Atamara I was split on. I've enjoyed both continents immensely throughout my playing experience and would miss either (hopefully they'd be frozen to be recolonized when player density increased). If our goal is to reduce density, I think something is to be said for keeping the continent with fewer regions, especially if Dwilight is kept already. With a higher density, the realms will divide into smaller blocks with faster wars and more internal competition between involved players. FEI has fewer regions too, but that also makes it harder for smaller realms to arise since they are so close to neighboring cities from the beginning. EI would offer secessions at least buffer regions between the border and their capital.