Need a sixth member for my Black team

Guys, I need help deciding a sixth team member.

I am using only Unova region Pokemon at the moment.

I sent my Archeops and Sawsbuck into retirement in the PC.

I currently have:

Samurott
Gothitelle
Chandelure
Excadrill (training)
Hydreigon

Please decide a sixth team member for me to train.

(I'm deciding between my Leavanny and Mienshao and I can't think which one to pick)