Like you said, they're both great, but I generally enjoy Summer more than Winter, and the sports they have to offer during summer, so I voted for summer.
I prefer the Summer Olympics over the winter counterpart. The athletes are more recognizable and I've always been more active in summer sports as well as prone to watch others participate in them. Michael Phelps, Missy Franklin, Misty May, Usain Bolt, these are names which will forever be imbued in my memory. World records are set and new champions rise to the top replacing the veterans of old. Moreover because the event occurs during a time when I am not in school I'm able to watch more footage and gain more knowledge concerning the participating athletes. That said I'm slightly biased against the Winter Olympics for the only one I clearly recall is the one from two years ago in Vancouver. I'll get back to you with a newer consensus in 2014, okay?