my personal references:
Final Destination: (I prefer Omega Gaur Plain due better ledges and better music) is a pretty solid stage for Jr when it comes with his Cart Game, however it should be banned when the opponent have easier time to zone you like Villager and Mega Man
Battlefield: this is basically BnB for Jr when it comes to his juggling game! the platforms are in perfect high for all Jrs aerials so you can easy juggle and score some damage! together that you can stage controll one platform with a MK!
however, its little harder with the cart game do smaller base platform and the opponent has more options, but its still easy to do! ban this stage if the opponent loves having platforms! Like Shulk and Sheik
Dreamland 64: (basically Battlefield but a honorable mention because my personally favorite stage with any character).
+ bonus the wind, it can sometimes blow away our MK but it can be a good thing if the opponent gets the MK in the face of the wind! the second hit will not connect but it will by us time to either attack or retreat!
also, the blastzone are bigger in this one and with Jrs pretty good (but gimpable without UpB Dodge) recovery, you will survive longer and gimp the opponents easier!
Smashville: (Best stage for Jr my opinion) has the best of boths world from Final Destination and Battlefield! the small moving platform can easy be stage controlled by MK while you are controlling the base. pretty much my go-to stage (if its banned, D64/BF or FD are my next to go to)
Lylat Cruise: can be a good stage for Jr thanks to the base platform isnt flat and 3 smaller platforms (which benefits us), I know many have problem with the ledge, but I dont find it too hard with Jr thanks he has good recovery and he snaps the ledge pretty quickly and easy! its great starter counter pick against opponent that requires vertical zoning Like Ness and Samus, I believe ZSS is having hard time on this stage thanks to that we have a roof from her DownB, her Paralyzer hits the tilting ground and she has harder time to grab/set up
Town and City: it can be a good stage thanks to its layout, but my personal opinion is I dont like this stage (I do good on it, but I have a grudge on the stage) so I often not selecting this stage. but its a wierd mixture between BF and Smashville in its own layout!
will write more later on counterpicks!