Marvel's precursor Timely had the All-Winner's Squad. Not the best name out there. Marvel definitely improved on things.  I think, Roy Thomas chose "The Invaders" because it fit well with "The Avengers" and "The Defenders" pattern, even though it's a somewhat negative term. "Liberators" might have been a better choice. On a similar tangent "The Defenders" fits Thor, Iron Man and friends better than "The Avengers". 

I thought of it in the same way as the Royal Air Force uses it: a flight is a military unit commanded by a squadron leader (a squadron leader is equivalent to an army major or navy lieutenant commander). 

I'm probably equally a DC guy and a Marvel guy, so I always appreciated the differences between the two.  "The Challengers of the Unknown," "Legion of Super-Heroes," "The New Teen Titans," and (use all the words please) "The Justice League of America"!

For Marvel, it's almost as if the names were an afterthought (the Ultimate version of the Avengers could be "The Ultimates" and still work).  At DC, sometimes the name was the main thing!  "Challengers of the Unknown" and "The Doom Patrol" are cool, awesome names that give a little thrill--I think the names are why these two concepts are never allowed to fade away!

(Same thing with Marvel's solo heroes--AMAZING, INVINCIBLE, INCREDIBLE, and MIGHTY [again] for Spider-Man, Iron Man, the Hulk, and Thor, respectively, while Dr. Strange and Daredevil both got descriptions AFTER their names.  But DC didn't do that with their solo heroes, but they DID give them plenty of non-cover nicknames like "The Mighty Mite," "The Scarlet Speedster," etc.--BUT that's a discussion for another thread!)

Used it in many fantasy leagues.

I like the Marvel names much better. DC's groups always sound like a bunch of super friends.