please state why you like/dislike them

well for most important i'd say its a tie between lungs, heart, and brain.
My favorite are the sex organs though ;o

Silly boi, wrists help to accelerate or decelerate a punch.

Ankles help with balance.

They are all important.

For me, the least used one is the neck joint. I usually keep it lax until the end.

My fave muscle: chest<---Power
Least favorite: Wrists, cuz they always snap off...

Most important: torso<---power
Least important: neck (although it is still pretty useful)

IRL:

Fav (Vaginal muscles)
Least favorite: toe muscles (they are weak and too dependent on each other)

Most important: hmmmm

Heart/sexual muscles

Least important: ear muscles

Most favourite: Glutes, they help angle a kick to where you want it to go.
Least favourite: Wrists, too easy to snap when you punch someone in MP.
Most important: Knee(s), the most used joint in the game for me.
Least important: Neck, I just leave it as is when I start a replay/match.

Fav:Knee:you cant kick ukes head off wif no knee
least:Neck what use is that for besides showoff?
Most importan:Knee ^ same reason
Least neck ^ same reason

Most favorite: Chest.

Least favorite: None.

Most important: Chest.

Least important: Everyone have a certain level of importance. Saying one is "unimportant" would be underestimateing it's purposes.

Favourite: Glutes

Least Favourite: Neck

Most Important: Chest

Least Important: Neck

All are, really.

Also being a wushu player i must disagree on wrists.
They are very, very useful if you want to comeback.

I agree with him.But :

Most Favourite:Chest Like others said...this is good when you need to change the situation

Least favourite:Neck You can do pretty nothing with it.

Most important:Chest (as above) or Knees The knees are the most important muscles IMO.They are used to do almost everything...

Least important:Neck (as above)