If I had my choice, Knuckles just because he's my favorite and...
-Uniqueness-Glides, Powerful punches, Could dig into the ground to create pitfalls, Hopefully able to crawl on walls
-Storyline-Brainwashed like in sonic and knuckles, making him a villian
But doctor robotnik would be pretty awesome
-His vehicle would morph depending on B's
-Naturally would have rockets for
-He would be very heavy making in both fox style and Bowser style
-He would have a huge hitbox
-He would be rather slow unless in helimode or car mode and DK or less speed with Osterich
Knuckles B's
-B-Charge up Punch (Charge it up like links arrow, but attacks area like captian falcon)
-forB-SOnic spinball (like sonics forward B
-DowB-Dig into the ground/create a pitfall
-UpB-Uppercut (like marths/Roys old upB)
-A attack type-His offensive moves (dashing, combo A, tilt, fair, nair, upair, Smashfor, Smashup) would be either quick or powerful while everything else has some lag time before or after making it a little less worthwhile using
Robotnik B's
-B-Fire small homing rockets (Do like 1-2 damage and stuns a little [more for starting up a combo or for stopping momentum])
-ForB-Car Mode (Use teh drill)
-DowB-Ostrich mode (run around on high legs with long arms)
-UpB-Helicopter Mode
-A attack type-Each vehicle has different attacks
but for the most part, each attack corresponds to where each vehicles weapons are
-Ostritch mode-Good for tilts and ariels (works like a mix of marth and DK with less priority or range)
-Car mode-Good for dashing/Edgegaurding (Car mode has no blowback so everyhit is a combo hit
-Helicopter mode- Good for upair, uptilt, upsmash
Every attack that Robotniks vehicle can't do while in a craze mode, he reaches out of the vehicle and does himself
His grab is a grappling hook
In other words,
-Robotnik must adjust to each situation
--When people are distracted/off the edge-Use teh Car
--When you are fighting one on one or any amount of people-keep a good distance with ostrich
--When people are in the air/you are off the stage-Use the helicopter
--And all the while Fire dem rockets to make sure that you can get more momentum and an attack without fear of them attacking
Inother words, the coolest character eva.
PS: I wouldn't want Shadow because he seems like a coperate character used only to support storyline/boost sales and it seems little to no imagintation was put into him