I mean, I have to go with Rändajad, right?
And to round out my top three: Yugoslavia 1992 (a true classic and the end of an era) and Italy 1997 (it was the first one that came to mind).
But honestly, this is an insane request, it's so hard to pick just three. There have been so many great entries over the years that even narrowing it down to 50 would be difficult. Honourable mentions for me would include the class of 2009, Croatia in the 90s, half of Italy’s catalogue, early and some recent French entries, lots of 2000s songs purely for nostalgia (even if I don't necessarily think they're good), Denmark in the 80s, and quite a few winners.