From best to worst.
Cudge - doubles damage, lets you move normal speed.
Dashell - Makes you much faster than Carrie.
Carrie - Makes you faster + can jump on spiked enemies and ride on spikes
Boomer - Like cudge, but delayed (if you detonate him early the enemy still might have escaped)
Thudley - Like cudge but you can't use him in low ceiling area (P of 100Ts)
Barry - Great for blocking attacks, but peachs parasol does the game thing, plus does lower damage than your attack
Thoreau - Kill 2 birds with one stone, can't pick up spiked enemies and useless for killing if no other enemies and no pits
Slim - Can't be hit when still and can be used for stealthy attacks.
Dottie - Like slim but harder to control and can still be hit.
Fleep - can't damage but can make enemies dizzy, some enemies and bosses aren't dizzy long enough or don't get dizzy at all
Piccolo - used 3 times in the game ever, only good for during cursya curses