after that if you like pvp, DO NOT buy more campaigns just for their skills (backtrack: you can only unlock a certain skills depending on what campaigns you have. Prophecies has A LOT of skills for the core 6 proffs, while the others have less for the core 6 but have 2 extra proffs you can play with.).
Buy the pvp unlock pack that will allow you access TO UNLOCK everything needed to pvp, you won't automatically have it, but you have the potential to get everything in game for pvp (for 20 dollars). If you love pve way more than pvp, get GW:EN
If your only going to buy one, proph has a good skill pool to work form, longes (some say most boring) campaign, good looking armor, but only 6 proffs. Factions has a STEEP learning curve (but you max out fastest), 2 extra proffs, best pvp content of the 3, but least pve content. Nightfall you get heroes, 2 extra proffs, most balanced length of campaign (note that if you don't plan to get NF but get the expansion pack, GWEN, instead, you get heroes from there too)
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