Hello,

Someone asked me the same question through private messaging a few weeks ago - from what I heard, as far as EU servers are concerned, Moogle has a very active French community while Shiva has a strong German community. Other servers are a bit more homogeneous, and Odin seems to be the most populated one (according to http://xivsoul.com/). Look around the forums and you'll see that it's pretty much the same everywhere - not a lot of interaction on the surface, most FCs stay in their own thread and advertise their needs when necessary.

However, Phoenix has the most active Lalafell community, take that as you will!