From a point of view of a person who now finally has all PWs, tested them all in the field, and considers PW as a main character, I almost completely agree with
@theLoneskull 's list with one minor exception - I still place Rusty above Blood Drive.
If this tier list is meant to reflect not only pure strength, but also endgame usability (in high PF streaks and Dia Rifts), buff conversion still wins over raw damage. It does not mean that Rusty will shred a Private Dick or Bio faster than Blood Drive, but she would be way more useful when dealing with M&F's Last Stand, G.I. Jazz, Overclocked, etc. Also, she's a Bronze, so she requires less investments to become an efficient fighter. So, if a new player is going to go by this tier list, I would say that in a long run choosing Rusty over Blood Drive is totally justified.
@Art3mes , since you already have Fly Trap, Buzz will not be a groundbreaker. After hundreds of battles with both, I decided that both mainly rely on their ridiculously high damage. Buzz's Heavy Bleed is just a cherry on top, but I yet have to see an opponent team where Heavy Bleed would allow me to do anything that 28K paper damage could not achieve.