The strongest I've seen is Tempest, Greatest Legacy, and Scholar. Once Tempest got Cleansing Downpour both Tempest and Legacy could heal Scholar out of turn, and he could use his power to Bring What he Needed, keeping a steady supply of cards. They effectively weaponize healing so that the biggest problem is the Scholar being too high on health.
Well, I'll start with the one on my list that's not going to get any arguments, and say "Team Leader Tachyon". Extra draws for the entire team? The only power she'll ever need being her innate? The ability to destroy ongoing and environment cards, along with great heavy hitters, multi-hitters, and one of the best villain debuffs in the entire game? Yes please.
My second choice would be Dark Visionary; she's usually just there to make sure that the big cards from the villain deck don't come out too soon, but Twist the Ether is also one of my favorite cards, sometimes played on the villain (especially on either version of Spite or on Gloomweaver's alt), other times played on my third choice to empower all their attacks... And that's a lot of attacks generally.
And finally, Omnitron-X. Seems almost every list on this page has an all-purpose hero, and most of you seem to pick Tempest for this... Personally, I prefer X. His components just allow him to do so much in a single turn, and his plating will usually prevent him from taking enough damage in one turn to destroy them. And then there's Disruptive Flechettes... If the villain has out multiple ongoings, there's no better card to play. On top of that, if you have both Twist the Ethers out, he'll be dealing 14 damage to the villain card each turn- potentially more with more villain targets out. Top it off with one of the best environment destruction cards in the game and an innate power that allows you to catch any double jeopardies that Dark Visionary spots, and I'd have to say Omnitron-X is my favorite go-to hero.
Of course, I might be biased about that last one, considering Mega Man is my favorite video game series.
Once we see the decks for Guise, Skyscapper, and Captain Cosmic the best team could easily change.
True, but by that logic, we can't have this discussion at all until Sentinels is finished.
I would swap out O-X for Argent Adept, there, but otherwise that's a really solid pick. I'd say:
Team Leader Tachyon
Prime Wardens Argent Adept
either Visionary, Parse, or -- for damage dealing -- Wraith.