Anyway: My biggest gripe about season six is a lack of stories about the trio, so I shall second (or third. Or fourth) that suggestion.
Dito. Personally, I like the brillant way they balanced the Trio out, making these characters able to carry nearly every story constellation.
(Longer explanations will follow once again..you have been warned
a) Fry/Bender Best Buddy
b) Fry/Leela Love interest
c)Leela/Bender Mere Coworkers or people not having much to do with each other, but
having to pull together on a certain matter.
The Trio can act as
a) a group consisting of all three
b) Two Characters, with the third taking a supporting role
c) One Characters, with the other two taking a supporting role as a group.
Also, with Leela mostly going for the morally correct sulotion, and Bender going the easy/most
profitable way, the writers can use Fry to chose one side (often tricked by Bender) to give that side a 2/3 majority.
(Allowing the Trio also to go for the ethnically wrong solution).
Every character constellation, every course of action is possible with these three characters. It's just the minimum number needed for that, and it works brillantly.
AND (that's my major point): By staying with so few characters, they will not have to act like a homogenous group, but rather as individuals, still staying true to their character.
(E.g. "Möbius Dick": It was Leela, and an anonymous mob. The "We've had it with you" could have come from any character. While with the trio, it would probably have been Bender to go for a mutiny first, with Fry letting Leela get away with her actions for the friendship's sake (until it would have been enough even for him, and delivering the "Okay, Leea...that's it". With that phrase delivered by the most lenient one toward her, showing much clearer that a border has been crossed, instead of a mob repeating several times "That's enough". But with Möbius Dick my least fav episode -predestined for my negative personal examples- you might wish to think of examples from other episodes
(Okay... I'm finished with my theory why I consider the Trio's character constellation to be genius