Most Helpful Guys
If this was Marvel COMICS, the most powerful, most well-rounded character would be Thor. (see graphic) So you'd naturally include him.
HOWEVER, in the Marvel Cinematic Universe (MCU), Kevin Feige, president of Marvel Studios, has already mentioned that Captain Marvel is the strongest character in the MCU, so you'd want her as well.
With the last $5, you'd then go for Hulk, if you wanted brute strength that, theoretically, has no limit.
5: Nick Fury
Hulk will toss Ant-Man into Thanos ass. Ant-man will now continue to ass rape while Groot is saying groot things. Black Widow needs to be there to cause Thanos distractions with her body. While forcing Nick Fury to say "I've had it with these motha fuckin' Thanos, on this motha fuckin' planet." line.
Most Helpful Girl
Captain Marvel, who apparently has every super power, Star Lord has no real powers but he's comic relief, Doctor Strange, Ant-Man, Nick Fury to find and recruit everyone else this budget didn't cover.