Where else are you considering apart from Paris? For me, a major problem with 'honeypots' such as Paris, Prague and Venice is that they are overcrowded and sometimes overhyped.
The villages perchées (hilltop semi-fortified villages) of the south of France are magical. So is Daroca in Spain; indeed. much of northern and eastern Spain. Alhambra is interesting but overcrowded, expensive, a little pretentious: another 'honeypot'. Mertola in southern Portugal is a fascinating mediaeval town with a true mediaeval street layout. Lisbon is good, too, especially Alfama.
As you might guess, my interests decline around the Renaissance, though I also appreciate Georgian (Bath, of course), Victorian (Birmingham, St. Petersburg, Paris), Edwardian (Delhi, Whitehall in London, though you'll probably be arrested as a terrorist for photographing the latter, and besides, like most architecture, it's harder than it looks), Thirties brick architecture and even some modern architecture -- though not much, and not the Le Corbusier school of 'machines for living' or Frank Lloyd Wright's self-indulgent stuff.
If you're in London take the train down to Rochester: run down, turning into twee with gentrification, but still interesting. From Paris, consider going north. Do not neglect Belgian venacular architecture: excellent Art Nouveau/Art Deco, especially in the detailing. Amsterdam is good but another honeypot.
And don't forget Bristol, famously the only city with a railway station for a cathedral and a cathedral for a railway station. In fact, most railway architecture is good...
Sorry. I could go on forever. Like you, I love architecture ('frozen music') but I find the stuff I like best when I am off the beaten track. Hire a car and... wander!
Cheers,
R.