Keep in mind, I don't consider myself THE authority on this game, there may be things I'm overlooking. This is largely what I've seen/experienced. I may be judging some chars too harshly, others too favorably. I think this is fairly accurate though.
Lastly, everyone aside from Pluto/Chibi is viable, and even those two have *something* going for them (even if it results from bad situations).
Jupiter + lariat, guard cancel 360 make it nigh impossible to jump in on her. guard cancel 360 will also destroy badly spaced normals + strong keepaway w/ thunder dragon and coconut cyclone + high damage off lariat combos w/ resets into 360 + strong oki
- slow normals/walkspeed (this is negligible, you wont be playing footsies too much) - super isnt very good (damaging, but slow startup/recovery, no invul... honestly you can just forget this exists)
Mars + 2 of the best, if not THE best projectiles in the game. fire snake (ground fb) is fast, recovers quick, knocks down. burning mandala (aa fb) travels at an angle that can be difficult to jump over. this pretty much makes her the #1 zoner imo. + good walkspeed, fast normals + damaging bnb + can easily corner trap people w/ fire snake + super does good damage even on block, can confuse people (looks like fire snake, but starts travelling upward)
- gc is kinda meh
Neptune + jab dp is hilariously hard to stop/punish. just do it. + good, safe oki + decent fb, not as good as mars though + good range on normals, decently fast
- has problems w/ the above two chars (gets fb trapped very easily vs mars, has a little trouble getting around jupiter's fbs)
Mercury: + fastest character, has one of the better footsie games + pretty good dp, though neptune's is better + has two fbs that function similarly to mars (again, not quite as good) + has a wall jump
- super is kind of awkward to use
Moon: + far jump combined w/ dash canceled air fb gives her a pretty decent left/right game... probably her best aspect.
- short range on normals - only really gets decent damage in the corner
Venus: + good reach on chain attacks + good dp + multiple fbs etc. see above.
- chains are fairly laggy - air to air is meh - painfully slow movement
Uranus: + has an infinite (!!!) + has a forward dash
- fb game is kinda poor - infinite is hard to set up, a lot of gc baiting etc is needed to land a clean hit - forward dash can be reacted to. blindly charging at your opponent will get you killed.
Pluto: + her super ranks among the best in the game. safe on block, can be canceled into, can be used as a ghetto forward dash... it has many useful applications.
- lp fb does not go fullscreen, hp fb only covers the space in front of her. don't expect to win fb wars too often. - laggy normals - only really becomes a threat at low hp
Chibi-Moon: + useful super (good chip dmg, covers the battlefield, once she gets started its almost impossible to move forward against her) + dives/instant overhead give her a decent mixup game + uhhh... she's moe?
- laughable range/speed on normals - terrible fb, you wont win fb wars. ever.
Jupiter is godtier
Neptune mars mercury and moon are high
Jupiter just has all the tools in the game and back turn light lariat combos do 100% off of any crossup you land.
Neptune has the best DP, and her super dp will do 70% life on counterhit, making it the best and most reliable big punish in the game.
Mars has sickingly good fireball lockdown and can confirm into her HK flipkick off anything for good knockdown and oki.
Mercury has the best LK and decent fireball and reversal options
Moon is the most mobile character and gets some pretty sick keepaway and mixups off doing air hearts during her dashes.
Venus has chain into up fireball lockdown, the up fireballs are insanely good and give you sickening plus frames on hit and block. You can link multiple of them in a combo and do her desperation move after one if you input it fast enough, giving venus access to the most reliable 100% DM combos. Also venus love me chain is a decent reversal tool. J7.HP is a pretty sick instant overhead. And up fireball into walkup throw/love me chain is sick.
Pluto is worthless without her DM, it recovers superfast on whiff giving her forward dash capabilities, and DM whiff cancel combos which can actually do some sick damage if you have the execution. DM whiff leads into sick pressure and mixups too, but you need to lose 50% of your life for pluto to start being a real character, making her have a lot of uphill battles.
The reason Uranus is lowtier despite her godlike training mode status is that her DC lockdown gets blownup by GCs, her fireball sucks ass, her forward dash has a super long duration and isn't invincible, and her normals aren't all that. You can shutdown her forward dash BS with a wellplaced fireball or LK and keep her out all day. But if she gets in she can infinite you so her matchups are all sorts of wonky. Bitch can't do shit versus fireballs that travel over uranus world shaking.
Don't play Chibi moon. Well ok, her DM leads to decent fullscreen chip setups, but that is a lot of chip you're going to have to deal in order to win.
I wrote this all out on my phone so it probably looks like shit, but there you go, my knowledge on the tiers from memory.