Vancouver 2010 in terms of the atmosphere (with a tear in the eye regarding the death of the Georgian luger). Also, Nagano will always have something special for me (my first Winter OG as a kid, staying up very early to watch luge and biathlon, only to find the events being delayed due to heavy snowfall, so ending up watching curling all night long xD), even though I remember that there were many claims about bad organization. I always liked Salt Lake City (somehow) as I remember great fights in CC, Nordic combined, Speed skating (mostly from the German perspective).
Unfortunately, the last two editions of the Winter Games are at the end of my personal ranking list. However, (I fear) Sochi and Pyeongchang will shortly be joined by this year's games as I never never ever had so less pleasant anticipation of OG in terms of the atmosphere and the host country in general.