My favourites are mostly gothic and romanesque:
In Britain: York, Westminster, Winchester (interior), Chester and Durham. Salisbury has a phenomenal spire, but I don't like the front porch (too wide and angular).
France: an abundance of riches, but in particular
- Amiens: soaring interior
- Paris: Notre Dame (not the biggest or highest, but perfectly formed and proportioned), and Sainte-Chapelle
- Chartres for the stain-glass windows, preserved for 800 years
- Caen: Abbaye aux Hommes (St-Etienne)
and Abbaye aux Dames (Trinité):
finest examples of Norman style circa 1070, commissioned by William the Conqueror and his wife to square their marriage with the pope (they were cousins). Actually, anything built by Lanfranc is usually very fine. In the same town, the late Gothic St-Pierre is beautiful:
The spire was brought down in 1944 by a single 16" shell from HMS Rodney, firing from about 15 miles away. The rest of the real estate suffered a bit too:
- Reims, where the kings of France were usually crowned, was heavily shelled during WW1 but has been well rebuilt, partly with US financing (Rockefeller family in particular).
- Albi, already mentioned upthread, is wonderfully weird and has a wild polychrome interior:
Favourite in Italy: Siena
In Germany: Mainz, Cologne (but 19th century spire), Ulm (ditto and seems a bit out of proportion with the rest of the building).