WvW ratings is a (very) rough guide for activity, you can see them here:
http://wiki.guildwars2.com/wiki/World_versus_World_ranking
It doesn’t mean that the top server is the most active or most populated, since there’s also the fact that some servers might have less PvE going on but higher rating because of highly organized WvW oriented guilds, but I’d bet that any server on the top 15 or so will be active enough. Take into account that the most active a server is on WvW, the more frequently you’ll bump into queues when trying to join, so while it might be a good idea to select a high enough server, also don’t select one so high that WvW is always so filled with people that you might not be able to play on it. You can guest on other servers to get a feel for it, but transfering costs up to 1800 gems (depends on how high the population of the server is), but you can do it for free if you delete all your chars and start over again.
Personally I play on yak’s bend, and so far it has been great, people tend to be friendly and there’s good player activity in most of the places I go to, at least late at night when I can play, and I see dungeon groups forming all the time.
BTW, the 10 days logging rule might be hard to enforce in this game, mainly because the guild management system still isn’t as good as in other games, mainly because it doesn’t tell you when someone last logged in. The guild I’m on (it’s a rather big one, though) had to do two mass kickings and reinviting to keep the number of inactive players low, but mainly because the guild roster was big enough that we needed two guilds to accomodate everyone (max guild size is currently 500 accounts), on the second mass kicking we managed to consolidate everyone in a single guild.
It’s a pile of Elonian protection magic, mixed with a little monk training,
wrapped up in some crazy ritualist hoo-ha from Cantha.
A real grab bag of ‘you can’t hurt me. They’re called Guardians.
