One of the best things are that these 3 sites are next to each others so you can visit them in one day if you want. I visited only in the cathedral and Alcazar. It was very cheap visit for me: for students entrance to cathedral is only 2 euros and entrance to Alcazar is free! The gardens were my favourite part in Alcazar. I think Alcazar is as interesting as Alhambra. In cathedral I liked the treasures that they had there.