Skyrim easily! So much more value for money in terms of playtime. And even if you've played it every freaking time Bethesda have released a different version, its still a completely new experience in VR. So worth it. Also, side note, its probably the best game for long play sessions to help develop your VR legs.
Skyrim... Or Doom... Or Mario+Rabbids... Or wait until other great/good games come out which you will most likely enjoy playing for hours/weeks/months.