Okay, I voted for 8 because with that number there are enough characters do allow major disagreements and upheaveal without completely leveling the team--like when Terra became the 8th member of the classic "new" Titans.

But eight is still relatively easy to remember and keep track of everyone.

Not a big fan of the "family" feel of smaller groups like the original Doom Patrol. Focusing on a few members each issue is okay, but the small numbers wear on me after a while.

And not a big fan of huge groups like the old-school Legion and some versions of the Avengers when you can't tell who's in or who's out or who is on which coast.

The team itself should consist of 5 (or 6) members.  There can be additional characters for sub-stories and relationships but when the team is in action 5 works best.

So my answer is 5 members that act as the team in that issue but the overall group can be larger where the 5 can rotate per event.

Anything above 7 require the team to split into squads whenever they do something, so why not create to books but let them interact freely between books.

I'd say I have to agree with 5, but I actually have a preference for building solo adventures when I can.... as many comic books featured a lone hero.

That's another factor... working. With the older gamer population that is a considerable fact. Groups tend to get to be a bit smaller because of such... and sometimes unpredictable as far as who can make it or not. V&V and the super hero genre in general is good choice for that sort of thing, in my opinion. As far as fantasy gaming goes, in low magic or lower level campaigns its hard to rationalize characters popping in and out of the party from session to session (hence the reason that the GM or another player usually has to pick them up and run them as NPCs). In a super hero game, there can be that distress call "Flamboyance Man! You're needed back at the station, report immediately!" and thus if Flamboyance Man's player cannot make it then Flamboyance Man can be removed (unless it upsets challenge balance) from the action in a sense that is legit with storylines.