I live in Paris, I have been to London, Berlin, Brussels, Amsterdam, Athens and Rome.
My two favourites are Berlin and Rome. Berlin because of the energy and just plain coolness, Rome because where else can you find so much amazing art and architecture within 10 or 20 minutes of each other, walking distance? And the food is amazing, of course.
Second in line are Amsterdam, Athens and London, all of them great, but London I found was really expensive. Athens is a bit behind Rome, but a truly lovely place to explore. Amsterdam is also lovely, accessible and very very beautiful.
Brussels is OK, I guess, but mainly for the people who I thought were very kind. Some places in Brussels are ok, but it's not as nice as Amsterdam for example.
Next in line for me are Madrid and Lisbon, I love Spain already and I can recommend places like Granada and Sevilla, which are totally amazing.
There is a guy named Arthur David Olson who maintains a small database of all the time zones in the world, including things like leap seconds and such. It's used by everybody and it is updated several times a year. See here:
https://en.m.wikipedia.org/wiki/Tz_database