My favorite thing about Renarin is that he's the most relatable of the characters, in terms of his similarity to a normal person. The main characters in books always get to spend the whole time plotting and fighting with other extraordinary, good-looking, intelligent people, and it's depressing to think that if any of us were to be inserted into the story, we would probably be completely ignored and sidelined. It's cool to have Renarin there, a relatively ordinary person who isn't quite so perfect, talented, and likeable, because we get to see how everyone interacts with him (i.e. Shallan is rude to him, Kaladin is generous, many people just disregard him).
I view Renarin's acts of bravery as more of an attempt to seize control of his life, though they are also brave. But sometimes he ends up just giving his brother and/or father another thing to worry about. Also, he did help Adolin out in that duel by running out unarmored and probably saved them.
Basically, I like Renarin because he hasn't had this charmed life where everyone loves him. He has had his own unique form of suffering, but you rarely, if ever, hear him complain. I feel like he (at least before the end of WoR) represented what an ordinary, klutzy nerd with limitations (aka myself) can do to be brave.