Liberty was always my "home server", though I also had a few characters that I played pretty often on Virtue and Union... Of the three, I was by far the most comfortable with the quieter community on Liberty.
Union had some interesting people to chat with, but I found myself mostly soloing as far as game-play went when I was there. It was a Euro server and I'm in Seattle, so there were just never many people on when I was. That made it very easy to pretend that Adammas and Niaera had the City to themselves, which had a certain appeal.
Virtue... Well, if I'm being completely honest about it, I didn't care for Virtue at all. I know many of you loved the place, but I found it crowded and a little too goofy. Those times when I tried to team with non-roleplayers, I ended up with total nutballs who were more about doing stupid things "for the LOLs" than actually playing the game. When I teamed with roleplayers, it wasn't much better. They'd stand around chatting in their SG channels or private groups (Even when there were others on the team who weren't in the SG or members of those groups, and so couldn't join in-) for long stretches of time, more or less ignoring anyone else who happened to be there. After the fourth or fifth time in row where I ended up spending half an hour standing around the lobby of an office building doing absolutely nothing but watching other people emote at each other, I sort-of swore off of teaming on Virtue, too. It's not my place to tell anyone who liked the Virtue culture that they were having BadWrongFun, but it wasn't my cup of tea.