Joker is a kind, easy-going, and cheerful  individual, who strives for the mirth of others, as shown when he intentionally drops balls he was juggling on his head for the amusement of the audience. 
Despite this outer appearance, though, he is very serious about his duties and does not easily give in to emotions.

Joker displays great care for the other members of the circus, but puts pleasing Baron Kelvin, no matter how abhorrent he finds his requests to be, above them.

A kind, easy-going, cheerful pierrot.

Felix is a person who does not exactly express his emotions. He is seen to usually be the quiet type who does not laugh, cry or speak a lot. He seems not involved in a lot of things and holds little to no interest in people and things, except for significant others. He rarely ever does anything productive and is usually the lazy type. Although he seems to care very little about his academic career, it is later confirmed by Luna that he worked very hard to earn enough money to go to college.