I would say that The Grounds is arguably the most populated map at the moment, since it is one of the starter maps of the patch and one of the first people will see. Some fluffs like to crowd around the entrance near the Lonely Cave portal, so you're sure to hear a few conversations and roleplay advertisements there. You can find plenty of roleplays in the other maps, though-- Eastern Pass, Seaside Grove, and Cherika Valley are usually quite plentiful with roleplays.
Keep in mind that the update is still fairly new and people are still looking to find their footing. What maps may be populated now may change in the future, but at present, I would say that you shouldn't have any trouble looking in the Grounds. Don't be afraid to explore elsewhere, though. Part of the setup of the new maps is to encourage exploration of the different maps. c: