i LOVE Adventure Time! :> there are so many great characters. Finn and Jake are both so GENUINE, and their friendship is awesome to watch. and the whole surreal post-apocalyptic universe of the show is just enthralling to me. and one thing that's great about it all is that the humor isn't offensive or juvenile, and a lot of horrible but all-too-common conventions and tropes are avoided-- for example, there are a lot of really cool/smart/developed female characters.
my favorite character is BMO :3 they are just sooo cute and imaginative, hehe. i really liked the episode "BMO Noire". oh, and i also have a huge appreciation for the character of B-MO partially because they are canonically agender-- which makes sense, because they're a robot/machine. but it's just cool that there is a character on a popular show who is referred to in-universe with both masculine and feminine pronouns-- for example, Princess Bubblegum uses "she" for BMO while Jake uses "he", etc... the show plays around with gender quite a bit through BMO! it's a subtle thing, but i think it's interesting. i highly recommend reading the section about BMO's gender on this wiki page:
http://adventuretime.wikia.com/wiki/BMO