Clarke despises Uther for the crimes he has committed against sorcerers, although he continues to give him and his son help whenever they need it from him. Granted, if he refused, he'd be fired and most likely imprisoned.
Clarke sees Gwen as a good friend, trustworthy and loyal, and he believes that she is a truly good person.
Clarke thinks Morgana is wonderful, powerful and a bit intimidating. He's always felt like there's something different about her, but he's never been able to figure out what. He's not as close with her as he is with ost of the non-royal castle residents, but he still sees her as a friend.
Clarke isn't great friends with Casper, and in fact, he does his best to avoid the boy. Something about him just gives Clarke the creeps.
Clarke thinks Aiden is a sweet boy, if perhaps a bit naive. Nevertheless, Clarke likes Aiden well enough, and has helped him out with stuff in the library from time to time.
Clarke sees Arthur as mostly an arrogant prick. However, the young Keeper knows that despite Arthur being an arrogant prick, he's not his father, and could prove to be a far better king.
Clarke thinks of Merlin as one of his good friends, someone who he can trust with most things, although magic is not one of them. He often tells Merlin that he should look for better employment, as he thinks the way that Arthur treats him is awful.
Sir Kay seems noble enough to Clarke, although he's only spoken a few words to him.