Let me chime in as a WoW player that has played on both PvP and PvE servers.

In WoW, PvP servers are free-for-all save for a very few introductory zones. This means that as you're running around trying to do a quest that should take 10min, it could be extended into an hour or more simply because someone wants to be a jackass and kill you repeatedly for no other reason than he knows it frustrates you. On the other hand, PvE servers save the PvP interaction as voluntary only, either by entering an instanced PvP zone or turning on a PvP flag that lets someone attack you wherever you are if they desire to.

My first several characters were a PAIN IN THE ASS to play because I leveled them on PvP servers. I never got close to the level cap because it really wasn't fun to spend 90% of my time dying or running away from some endgame character that wanted to mess with me. Once I switched over to a PvE server, it was like being in heaven. Wait, you mean I can do a quest and NOT have to retrieve my corpse every 30sec? Sign me up!

Of course, we don't know a ton about how AoC PvP vs. PvE servers will be set up, but I'd be willing to bet they'll follow a similar model. I think joining a PvP server and setting up a PvP faction within the PvE guild is an interesting idea, but I'm not sure how well it will work. Toward the beginning, your PvP people will be spending time making themselves ready for player combat, likely leaving the pure PvE players exposed. You also run the risk of your PvP people becoming bored and listless. I mean, I'm all for protecting my fellow guildies, but I don't relish the idea of spending my 4-8 hours a day on the game following around John the Newbie in case he gets attacked while questing. :P You also have to consider the idea that your PvP exploits may result in retaliation against your PvE players.

One last thing to consider is that, going off of the WoW model, PvP and PvE do not mix well. Each area tends to require different skills/talents (game-wise, not player skill), and a person who specializes in one type of play will likely be deficient in the other, sometimes greatly so, all simply because of how they designed their character. Some people can afford and have the ability to adapt between the two arenas of play, but most won't. So really, it tends to come down to pick a direction and stick with it.

Of course, this could all be bunk once we see how AoC is actually set up. :P However, from what I've read, I'm not seeing a whole lot that's different from WoW or any other typical MMO. The leveling/class system is different, and the combat system is new and innovative, but it's still going to come down to getting weapons/armor and putting points into different abilities. Inevitably, those pieces of gear and abilities will fall under either the "suited to kill monsters" or the "suited to kill players" category.

If there's a pretty even mix of players who desire PvP versus players who desire PvE, the safest bet would be to join the PvE server (again, depending on how AoC sets up the servers). That way, the PvE players don't get ganked every 2sec, and your PvP players still have areas to go for the conflict they want. It's really the best "please everyone" solution there is. I can pretty much guarantee you that if the PvP servers are indeed free for all madness, the PvE players will become very unhappy very quickly.