I feel like we need to have a separate tier list for how useful characters are (both carries and supports) for people with low-mid tier gear collections and limited augments. Some characters are useful at all levels and very good late game (like AO Batman), but others are honestly underwhelming and quite mid at lower fusions with no augments, while being great when fully maxed and augmented (like Blackest Night Doomsday). I feel like it's easy for experienced players to forget the new player experience and how slow it is at the beginning. I don't even remember playing without Tantu Totem/MDC at this point, but for newer players that's the reality and it will be for almost a year, especially if they get a bad MP cycle. So I think a lot of the recommendations on here are great for veteran players, but they can actually slow down new player progression if followed completely. Even if they don't, I think they take away from the player experience and make it more "grind" and less entertainment.
I don't really have a complete tier list in mind, but a few characters I think have really been helpful at early stage (even if they were suboptimal later on), and should be promoted heavily and early on despite not being top carries:
Jessica Cruz Rebirth - Honestly the first thing that came to mind. Yes her SP2 is really long, and has bad damage distribution. But as a new player, you don't have top level gear, you don't have crit augments, and you don't have gear shatter either. She has great basic attacks that low tier gear can boost greatly, and she has excellent synergy with silver and bronze green lanterns, making her a very safe/reliable, if not efficient carry for newbies. She's also fun and easy to play, and her special hits at close and long range (sp2). The saw at end of sp2 also pairs well with any DOT gear. I think promoting her frequently and early is actually better than focusing on cards like Arrow/Green Arrow, because she relies less on top rate gear to win battles, and she has a much stronger basic build.
Teen Titans Raven - Again, her SP2 damage distribution is not optimal, but the high chance for 25% health damage after a SP2 is really useful for phantom zone bosses (just play her and 2 jokers and hope to get lucky, this is actually probably one of the easiest ways to beat elite phantom zone with no gear and low tier characters). She's also pretty fun to use and synergizes with WW 600.
Batman/Flashpoint - Not a top carry at the highest levels (unless supporting death stroke), but I think he should be prioritized above all else when obtained. Huge crit potential, great basic attacks, powerful special 1 with stun and no damage reduction. Bad sp2, but beginners are using him for basics anyways.
Arkham Knight/The Arkham Knight - Great basics, cool special 2 with an easy mini game (for non-button mashers and speed swipers) with extra damage. Again, not ideal late game, but for the early game, he has good synergies, he's relatively cheap, and does well.
Hawkgirl/Regime - Not needing crit augments to get a fully critical SP2, special disable, and cheap promotions. Not the best MP character, but useful for the early grind until you can get better gear/characters. Also drops from 200 nth metal pack frequently, which is probably what you should buy at the very start anyways (until you have an ok roster, metals are not that useful).
Deadshot/Suicide Squad - Less about promoting him, but he's easy to obtain from his challenge, and has easy mini games with a good combo ender and basics. Very fun to use and I think he's an enjoyable card for a beginner or a late stage player without needing crazy gear.
Nightwings (any variety) - Super useful due to the power drain for getting past early battles, I think using some credits to promote them is worthwhile for the early game and mid game.
Raven/Prime - Very very useful for beginners. The cheese potential is unmatched with health swap, plus that SP2 is not bad either.
Harley Quinn/Animated - Probably every beginner should buy a copy. Great support. Also pretty good late game.
Static - Good passive and survivability. As a beginner, speed is not the concern, winning is. Also his special animations are cool and he attacks fast, making him easy to use.
Great Carries when maxed (bad without gear):
Doomsday Blackest Night - Terrible damage-health ratio, SP2 damage distribution is suboptimal without augments (damage+crit), mid basics, SP1 doesn't do enough without augments. He's not terrible, but Jessica Cruz or Raven would honestly get you farther if you don't have doomsday augmented.
Bane/Luchador - One of my favorite carries, but he just doesn't do it when you don't have the gear. He's also extremely squishy, so he's not reliable unless you have the gear and setup.
Deathstroke Arkham Origins - He drops in one pack and it costs a bunch of credits to buy each one. As a beginner, I feel like the credits are better used elsewhere. Also, his SP1 is really hard to hit, doesn't even knock out reliably when at 200% unless you augment/support/promote high, and his SP2 is nice but mid without Arkham Harley Quinn as a support. He's an endgame goal.
Raven/Regime - I just don't think beginners will get much out of her. She needs gear.
Bane Arkham Origins - His basics are just so awkward. I get that he's great with good gear and everything, but before you get Tantu/MDC/Ras Al Ghul's dagger you have very few ways of having power quickly.
Deathstroke Flashpoint - Kind of bad without a flashpoint team, the specials are just mid without support of Batman/Aquaman. Good basics though! Love him now, but it took a long time to crit augment him, get the flashpoint team up, and actually get enough copies to use him successfully. Batman Flashpoint is way better early game, because he stands alone.
New 52 Wonder Woman (and all Wonder Woman Characters) - SP1 carries are great because they can KO and deal massive area damage with their SP1. Unfortunately, unaugmented, no-gear SP1 carries are really not so fun to use, and do not KO instantly. Middling basic attacks, relatively expensive to promote, SP2 is kind of good but not great. Getting the Wonder Woman basic attack chain to SP1 also may not be that obvious for a beginner, and her attack speed is not the fastest besides her SP1. I do really like her power back passive, and think she's good as a support for a starting player, but I don't think she should be promoted first.
Great Carries that don't need gear:
Batman AO (with an *) - The one caveat is that he is expensive. I kind of still agree with Skopos that Doomsday/Prime is cheaper and better for beginners. Also, the willpower to save up 370K credits or whatever is pretty crazy when you're a beginner getting maybe 1000 power credits a match, tops. Most casual players are not grinding the same battles repeatedly fast to get power credits, and sense of progression is important.
Doomsday/Prime - Good passive for beginners, also scales pretty well to end game. The passive sort of mitigates his middling basic attacks. Cheap.
Batman/Blackest Night - In my opinion, probably in the top 3 of best cards in the game overall. Just crazy good SP2, SP1 is useful for applying DOTs, great passive, great basic attacks, pairs up super well with hawkgirl (who makes him pretty safe to play). The block breaker chance with blackest night characters and smooth animations make him so fun to play, I think that alone should make him a priority. But...he is really expensive.
Deadshot/AO - But he is really hard to get, so I don't think he should be a priority target. One copy of him is not gonna take you that far.
However, I actually think Jessica Cruz should be prioritized over all 3 of these if she can be unlocked early.
The Batman Ninja Team...
My take about them is that they are actually pretty good for beginners. Catwoman in particular is easy and very fun to use, and gear is not really needed for them to be good. However, I don't think they should be promoted, because promoting them is expensive and messes up stuff later.
I get these are kind of controversial takes, feel free to disagree, etc. I just wanted to kind of give my alternative perspective to the prevailing meta takes, I think how easy to use characters are and how beginner friendly they are is important when considering progression, not just optimal builds for pros creating new accounts. And also, I think people should really find their own path as well sometimes, it's not the end of the world if your BN Batman is one promotion too high, or you use a suboptimal carry you enjoy (like a regime/superman or a regime/hawkgirl or martian manhunter or whatever else is out there). I feel like the golden middle ground is knowing which carries are the absolute best, which gears are the absolute best, and getting them high, but not optimizing every last detail. Thanks for reading if you actually made it here, I 'm really glad this game is still alive and I've been playing for 7 years strong (or something like that) now, and I still find new things about it very often.