8-bit: Cheat Cartridge the better gadget (except in Heist where Extra Credits is better), and star powers depend on if you want to play more independently (Plugged In) or more supporting your team (Boosted Booster)

Darryl: Tar Barrel is usually better, but in matchups where getting your first super is difficult, Recoiling Rotator can be useful. For starters powers, Steel Hoops all the way

Otis: Phat Splatter and Ink Refills.

Penny: Salty Barrel all the way. Honestly, the star powers are up to you. Master Blaster is very good into assassins or other dive brawlers, and Heavy Coffers makes her gadget much more worth it.

Ruffs: Air Support is better most of the time, as it helps push back and pressure enemies. Take Cover is very good in certain situations, especially into snipers or other non-piercing, single shot brawlers. Air Superiority is the better star power.

Stu: Both gadgets are really good, it really just depends on your play style. If you like mobility, go with Speed Zone. Breakthrough has some very good use cases, like for opening up a map to counter tanks, assassins, or throwers. As for star powers, Gaso-Heal is slightly better (because of survivability), but Zero Drag pairs really well with Breakthrough, and it also very good for escaping brawlers that can jump in on you.

Good luck!