So due to the lack of knowledge in how I played the game, before finding this site, I have champed all of the 3*s in my roster, the last coming this morning in the form of Hawkguy, totally fun. Now when I look at the vault, the only ones that I don’t have champed are Thanos, Squirel Girl, Spider-Man, Sam Wilson Falcon and Rocket &Groot. The only one that I don’t have a cover for is Spider-Man.
If the roster in your signature is up to date, you have time.If it were me, I’d plan on champing all of them over time, and I’d probably champ them in the order I get them fully covered.
In general, Thanos hits really hard for less self-damage than you think (assuming black is at 5 covers). Rocket just hits hard, and while not top-tier, is a strong character. Falcon is situational, but his combination of boosting friendly tiles and eliminating enemy ones is decent; his recent rework was pretty good. Squirrel Girl is… OK (her purple hits hard against tile layers and her green is certainly entertaining). Spider-Man is in desperate need of a rework, but cheap stun has its uses.
Sounds about right (might do Falcon first as his rework made him useful but then Rocket has true-heal so can stay fighting longer). Thanos as top priority is no brainer. When he has 5 black and is championed he will bring havoc to Lightning Rounds and early PvE rounds (just kill one toon and the rest dies as well). For grinding you can pair him with any true healer.