You can play PvE with anyone who has the factions campaign.
You can play PvP with anyone.
I quit quite a while back, but I'd assume the most populated PvE campaign would be Eyes of the North, then Nightfall, then Prophecies, then Factions. In Factions I'd guess Kaineng center to be the busiest area.
You likely stopped playing because the PvE feels like a chore and the game isn't updated often enough to make PvP less of a stale joke.
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