Parent Child Relationship setup or BoB or assignment rules

Hello all, I need some feedback and input.

What is the best way to set up accounts so that the person at the top(regional/district) manager sees all the accounts below them will allowing the user/owners see their own accounts and accounts in their region?

For example.

Bill, the regional manager in a territory that covers central USA has 20 accounts in his region.

All of these accounts are owned by multiple sales reps. 

I want Bill and the reps to be able to see all of the accounts in the Central region only.

Currenlty we use a combination of BoB and accounts assignment rules to make this work for