I voted for 2012. Couldn't relate less with the content of the lyrics (although they're catchy) but instrumentally it's very well accomplished, blending appealing contemporary pop with a taste of folk arrangements. The vocal melody plays an important part as well. This entry certainly stands the test of time, sometimes I'll wake up with it playing on my mind even though it's been almost 2 years now.
I also like 2002, 2005 and 2013 as my "post your top" threads can attest. Having this said, I still think that the best Greek entries in Eurovision come from the 90s.