Which of the following pokemon would collectively make the best team?

NO Ultrabests/Legendaries

Use the pokemon below in addition to the pokemon in pic related.

>Sandslash
>Muk
>Poliwrath
>Crobat
>Steelix
>Houndoom
>Kingdra
>Aggron
>Shiftry
>Flygon
>Banette
>Dusknoir
>Toxicroak
>Rhyperior
>Cofagrigus
>Klinklang
>Chandelure
>Greninja
>Dragalge
>Toxapex
>Salazzle
>Minior
>Dhelmise

Which team of 6 pokemon would make the best competitive team?