The best polymorphing form for a 10th-level outsider wizard?

[Shin Okada]

In the next adventure, I will use a 10th-level Shade (outsider) wizard with a Hell Hound familiar. Both the shade wizard and the familiar is a 10HD outsider. And the wizard's caster level is 10th. He can cast Polymorph spell.

Assuming they are fighting in a dungeon room, what is the best polymorphing form for them?

 

[Neonchameleon]

Depends what exactly you want to do and what sources are legal in your game - but check the guide.