It's summer, I'm a teacher, and I feel like writing a bit about sentinels. I've played far too many games, 3-5 per day on the app, and 3-ish solo games a week, along with a weekly session of 3 or so games. I've played everyone to excess, though some less than others. This list, as such, changes a lot. There are no bad characters, but I think there's still, more or less, an order to their quality. Consistency and power level when optimized are often at odds, along with very different ways of playing heroes based on both starting cards and specific villains create quite the push and pull in these rankings, but here's my attempt to order everyone, from worst to least (otherwise, where's the suspense!?).
52. Dark Watch Setback - The real problem is this Setback very often has no real use for his power phase. If he doesn't see the right cards, he simply does not want to lose 1 unlucky token, as they power everything else he does. That leaves him often skipping a lot early, and incredibly prone to ongoing destruction. He's a bit of a mess without someone to really feed him cards and doesn't add anything I really want in Setback.
51. Prime Wardens Captain Cosmic - A common thread amongst my lower ranked heroes is a largely useless power phase. Against a few villains/enviorments, you can make sure a construct is destroyed, but more often, his power phase is wasted on a potential benefit that never comes. He badly needs his PW mates extra card plays to get anywhere, so in nearly any other team without a top tier hero, he isn't worth it.
50. Freedom Six Tempest - Tempest draws a ton of cards, so why on earth would I want to destroy his cards to draw more. This does let him search for answer cards, particularly ongoing destruction, but at that point, he's getting most of the same benefit from just skipping his turn.
49. Prime Wardens Tempest - This is the point where the powers go from generally useless to not as good/have a big downside. In this case, three card plays can be huge, but the damage cost makes it prohibitive. He's made to work with his team, like PW Cosmic, being fed draws and playing out cards until massive healing comes, but since he's all but useless in the power phase until he sees a new power without his specific team, or at least specific teammates, he remains lower ranked
48. KNYFE: Rogue Agent - KNYFE wants to deal damage, but this KNYFE just manages to flail about uselessly a bit too often. She is good at tossing obnoxious villain cards that others have put at the bottom of the deck, I'm looking at you Jail Break, but otherwise, she takes too long for a glass cannon without some fairly major luck.
47.Ra: Horus of Two Horizons - This really changes the evaluation of Ra's cards, as he really likes his ongoings and extra powers far more early. The card search is really good, but here, any ongoing destruction is a huge setback, as Ra can go turns without dealing major damage... and really, Ra doesn't do much if he isn't pumping out damage. To use this guy, one should always try and keep a back up power in hand, and, really hope for a longer game where this Ra shines.
46. The Eternal Haka - He's got the same basic issue as Horus Ra. He draws like mad (especially if chucking Restoration and Shielding, do not chuck Battle), so he should see his powers, and his regular card plays usually have a draw rider, too. With these, and his natural Haka hit points and healing, he ends up working pretty well unless the player has very bad luck indeed.
45. Bunker - The lowest standard hero. I've played him as much as I have anyone, but he too often spends turn after turn waiting for something useful to do. His draw power is nice, but he, being a core hero, has a few more mediocre or very situational cards as compared to newer heroes, and can get stuck sitting there, awaiting good cards to play. Add in that equipment destruction can utterly destroy him, and he's just too situational for me, especially given both his alternates offer something different that his base power cannot.
44. Captain Cosmic - I really like Captain Cosmic. He makes the game easier for all the other heroes, but he's a bit subject to the whims of chance. Too many of his constructs are situationally useless, but his power does allow him to cycle into the needed ones far more quickly. It frustrates me to no end that he's a support character with little to no way to handle opponents problem cards. I almost always win games where he works, but there are far too many where he feels tangental to the end result.
43. Dark Watch Mr. Fixer - This guy deals such great damage, it's hard, like Cosmic, to see him so low. He needs a good draw more than most though. If you see nothing but Styles and have one you want to keep out, you have to hope someone else has an extra card they don't want destroyed. That difficulty drops him a fair bit, but his use of Tools is second to none, and if he can keep really any tool out, he ends up doing a huge amount of work.
I'll break here before my computer shuts off or something and I lose all this writing.