You know, I haven't done this meme because I don't really think in the hero/sidekick paradigm, I guess, so I was having trouble coming up with them. But I love ALL the characters you listed, to distraction (well, I don't know Dr. Who, but the others) -- especially Matthew and Marshall though. Great choices.

I don't have a top 5 list but have been intending to do a whole post in answer to this on Irene Merryweather -- who is Cable's assistant, which means she has the worst job in the Marvel Universe (except possibly Doc Samson, who is the Hulk's therapist). She works for a megalomaniacal busybod who has the inconvenient habit of being right most of the time, and might actually be the messiah. She also has the bonus of being in love with her boss, who is never going to love her back, because she is too capable and competent, and he can only be in love with people who need him to save them. *shakes head*