@VinMcCarthy This was difficult. I wanted to say Igneel originally, but I had to ultimately choose Ur.
She possessed great power, enough to even defeat a demon of the book of Zeref by sealing Deliora away. She faced great pain when she was told of her daughters death and yet still took on Gray and Lyon to train them in the art of Ice Make magic. She had both physical and mental strength to carry on even though everyday she thought of Ultear. I admire her strength greatly.
She even had the strength to give up her life in order to ensure the safety of her two students, as well as to seal away the darkness in Gray's heart.
She is one the reasons why these two are so strong. I think it would be amazing to have Ur as a teacher.