I'm fond of Canada, but I also really like the UK (cool looking), Mexico (also cool looking), Germany (fave EPCOT restaurant, plus the caramel place) and Japan (pretty, plus I get my lucky cats and last time I did the pick-a-pearl thing and I really like my pearl necklace)
I'm partial to the beauty and food of France. But I do love Japan and Italy as well, and the UK and Morocco pavilions both host some of my favorite character meet and greets. Still I think France reigns for me.
The Mexican Pavilion is my favorite. I love the outside of the building itself. The shopping Marketplace style is great. The San Angel Inn is a fantastic restaurant and the Gran Fiesta Tour starring the Three Caballeros is a fun boat ride.
I think my favorite is Japan, because of the food and the big department store. But the Canada pavilion is so beautiful, and Mexico is really pretty as well (the pyramid inside the pyramid??? Very cool.)