For longevity, I'd pick ESO. The world is massive - perhaps 50 times the size of Oblivion and Skyrim. It is also dynamic in that the world does not revolve around you; rather, it grows and evolves. Though it's multiplayer, it is extremely friendly to those who enjoy single player. Buffy 'outgrew' Oblivion after about 4000 hours. Same with Skyrim. When I added up her ESO time last year she was over 10,000 hours there and, a year later now, still sees no end in sight.
--------------------
|