Artemis is the most populated, and so it goes to reason that it has the highest population of non-retarded players. But it also probably has the highest population of retarded players. Dueling isn't much, especially not in RoM where fights last mere seconds when geared.
PvP server has full-stop open PvP anywhere, any time after level 15. You drop items from PK deaths. Its not recommended for people who don't enjoy PvP. Sadly, 90% of people on PvP servers do NOT enjoy PvP, but roll there thinking they're bad ass PvPers. So, you hear non-stop whining and complaining about people dying in zone, world, guild, whatever chat, and it really gets old (for me, at least). I have all chat except party and whisper turned off. Even people in my guild annoy me with their complaints about getting PK'd, so I keep that off most of the time as well. Diamonds are pretty much a necessity on PvP server, so you'll either be farming a lot to buy them with in game gold from AH, or spending a couple hundred dollars (or more, depending on what you want I guess). Don't know how things are on PvE server, but end game PvE bosses have a lot of AoE damage as well, so you'd still probably need a decent amount of fusion stones.