Amsterdam. Because of the cycling infrastructure.

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.

Even though i am german myself, i think i'd have to go with Berlin too. Berlin in summer that is.

Otherwise probably Rome or Lisboa. But capitals seem rarely the best cities of a country to me.

Ljubljana, with Copenhagen as a close second.
Those cities are just so relaxed, chill and interesting.

I've been to Paris (my least favorite), London, Berlin, Amsterdam, Stockholm, Oslo, Copenhagen, Ljubljana and Helsinki. Now that I think about it, I don't travel to capital cities much. They're usually the worst part of a country.

I've been to London, Dublin, Paris, Berlin, Amsterdam, Vienna, Prague and Copenhagen. My favorite is Paris. If you count Edinburgh or Barcelona as capitals, they would both be higher though...

I like Berlin and Lisbon. Luxembourg is also nice. I kinda liked Copenhagen but not as much. These are actually the only capitals I've been to, come to think of it. Well I didn't mention amsterdam but I'm Dutch.

Probably andorra de la vella. It doesnt feel like a capital(which is a positive for me) and the nature arround there is extremely nice. If its actual capital city like places then I pick copenhagen, stockholm or berlin.

Well, I found Berlin some decades ago quite impressive, culturally. Don't know how it is now, but via via I was told it's less relaxed. Prague for was then very nice, and not too touristic.

But, like Bruges ( and Gent) in Belgium, are so, I don't know, nice, relaxed and pittoreske 2b at.

Bruxxelles, London and Paris are just street & metrowise a mess. If you are OK with that though, and know the places to be, and you can find your way, your experience can be very special. What really helps in those big cities is to have the company of some locals (friends,). That would definitely amp up your experience in some of the "bigger" European cities, imo.