From the ones you listed my favorites are Exodus and World Killer. I also have a soft spot for Roads Taken. I remember bawling my eyes out over it when I first saw it as a child, and no matter how often I see it again, it always makes me cry, especially the part where Quinn and Maggie's life is shown in the Bubble Universe, and Thomas, their son (who will soon be made never to exist) narrates. I don't know how this scene came off in the original English version, but in the Hungarian dub, it's very powerful and emotional. It's strange because I'm not a Romantic person, and don't care for Romance movies, but somehow this episode always has this effect on me.
Wow! There's 13 worlds there I've never heard of!
Mardi Gras, Buttonwillow, Rollerblade, and Lemoore world is only mentioned off-screen.
Sitting Moose, Edison, Public Transit, Forest, Spiderwasp, Romani, Cannibal, Ice cream, Corporate, and Nude worlds are only explored for minutes at the end or beginning of episodes.
Cuban Missile and Pastiche worlds are from a fanfic series, I think, related to the creators of the website
earthprime.com
Oh, and I love Season 4, but hate Season 5 with a passion. I wish Jerry and Charlie stayed with the cast, and they continued the storyline of Season 4. Finding the real Kromagg Prime, meeting Quinn's parents, getting the anti-Kromagg weapon (not like depicted in Season 5), liberating Earth Prime, finding Wade (not like depicted in Season 5), and infiltrating the world the Kromaggs used as a base after they were banished from Kromagg Prime.
Anyway, my favourite episodes would be The King is Back because Rembrandt is my favourite character.
It's hard to pin down my favorite character, I think it depends on which Season we look at. My ultimate favorite was Maggie, she seemed to have the most "Eastern European" personality from all the characters, and most like the one I could relate to. She also resembled my Mother both in looks and personality. From Season 1 and 2, Quinn was my favorite, from Season 3 I liked Arturo the most. Wade was likeable through all of the three seasons she was in, perhaps she was the one whose personality changed the least.
Season 4 brought a lot of improvement and depth for all of the cast, except Quinn. I think I liked Remmy the most from that Season.
Although I don't like Season 5 like I said above, I had some sympathy for Diana in those episodes.
Colin and Mallory seemed pretty one-sided characters, though both revealed their more complex characteristics in later episodes.