Hella boring day, so I thought I'd do this.
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).
That said...
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.