Gallifreyans and humans, two races so disparate they have little in common on the surface, yet the Doctor, both Gallifreyan and a Time Lord, prefers the company of humans over his own kind.
The Time Lords have become insular, set in their ways, so sure they’re always right. They don’t allow mistakes, or admit to them. Humans make mistakes all the time, but they’re constantly learning, whether they realise it or not. They have such potential.
Being around them is refreshing; they see the universe with new eyes. The Doctor thinks he’s learning as much from them as he’s teaching.