Atlantic has several good guilds, so I'm sure you'll have no problem finding one that suits you.
United We Fight is an adult PvM guild. We offer nightly hunts, including lots of champs, peerless, doom gauntlet, etc. We're a rather large guild and members from all over the world, which has its perks: there's almost always someone doing something.
UWF isn't big on rules, either. We realize that, first, we're adults, and second, we're paying to play. The emissaries pay dues, too...we don't want to be ppls parents.
Our basic rules are: 1) don't PK guildies, 2) don't steal from guildies, 3) keep guild chat at a pg-13 rating, hehe.
Again, there are many options to choose from. UWF doesn't meet everyone's needs (and of course, you're welcome to have toons in many different guilds). That said, I really enjoy it and appreciate the friends I've made there.