If you don't want to be misinformed, the best way to know the most beautiful Spanish city is by traveling to Spain. That way, you will see things for yourself and be exposed to the true nature of things, plus you will get to meet the locals who will be truthful to you about this. The essence of this is to let you know that there are beautiful cities in Spain.
This means that people's judgment of the most beautiful Spanish city will naturally come based on how each city treated them. However, while there are so many beautiful cities in Spain, choosing Madrid as the most beautiful Spanish city is still a right judgment.
First, Madrid is the capital city of Spain and houses different architectural designs and structures that are absent in other cities in Spain. Madrid is also the home of different kinds of art designs, and you will definitely get exposed to some of their traditions and culture. Other beautiful cities include Barcelona, Valencia, Seville, Bilbao, Granada, etc.