Not to be a pretentious c0ck but it has been done a few times, but before it gets closed here's my all time Dream Team;
Elijah Snow:
(Planetary) -Leader/Director-in a Henri Bendix/Nick Fury role, brings contacts plus analytical skills to the table-
Emma Frost:
(New and Astonishing X-men) -Team Telepath, plus general ***** and flirt
Iron Man:
(Invincible Ironman + Avengers) -Technology interface, but engineering genius, can act as Swiss-army of the team i.e. a sort of Deus ex machina
Flash-Wally West:
(Flash and J.L.A.)-My favorite of the Speedsters, written how he was during Morisson's respective runs on J.L.A. and Flash.
Wolverine :
(X-men, New Avengers)-Berserk er rage , will be there when the shit hits the fan, plus there to do things the others won't
Rorschach:
(Watchmen)-Detective work plus brings lateral thinking to the team. I have chosen him over Batman as Snow and Bruce would likely clash.
Kitty Pryde:
(New X-men, Uncanny)-Loved her during Joss Wheeldons run, great powers + acts as teams moral compass.
Superman:
(Action Comics, JLA).- Indestructible team power house, strict moral code makes him perfect field leader, also there to fight off Alpha level threats, and perform feats on a Godlike magnitude (E.G. if a meteor is about to hit earth you direct him at it ).Ethical conflicts with the likes of Snow and Wolverine make team more interesting.
Ray Plamer The Atom
(The Atom, JLA)- Brings immense Knowledge and expertize to the team, plus his power makes him very versatile in combat and black ops scenarios.
Reserves;
Green Lantern Hal Jordan
(Green Lantern, JLA)-Doesn't make 1st team as he is usually insubordinate, and opinionated. Power Ring makes him ideal substitute for Superman and Iron man.
Plastic man
(JLA)- Doesn't make team, as lateral thinking skills will clash with Rorschach's, plus his humor is likely to irritate other team members, and Snow. Power makes him incredible versatile for both Black ops and combat.
