This is a great document from the IOC with images of all the Winter Olympic medals (it's a PDF, be forewarned):
My favorites include St. Moritz 1928 (gotta love the old-timey looking figure skater!), Grenoble 1968 (that was an Olympics with AMAZING design overall), Nagano 1998, and Vancouver 2010. Of those, Nagano looks dated to my eyes now but I think it well captures a sort of late 90s design aesthetic I'm nostalgic for. Vancouver 2010 I love, but I suspect will look dated in 15 years or so, so we'll see how I feel then. Grenoble might be my favorite overall.
I think my least favorites are Sapporo 1972 and Sarajevo 1984, which have a really similar look that I think is horribly dated and not very pretty. Albertville 1992 is also kind of a lowlight for me.