Ultima Online - Private server, 2 months.
Ragnarok Online - International server and some privates, 7+ years
Lineage II - Private server, 5 Weeks.
World of Warcraft - Vanilla and 1/2 Burning Crusade, and 3 months on Elysium server.
Dofus / Wakfu - 1 Year.
Guild Wars 2 - 2 Months
The Secret World - 1/2 Year.
Wildstar - 4 Months.
Tree of Savior - 1/2 Year.
Albion Online - Still playing.
I enjoy both. PVE is a bit more important to me though. I can deal with a game not having PVP, but poor PVE content ruins it for me. For PVP I generally prefer arena style scenarios more than large scale group PVP. Open PVP can be fun in small groups tho.