Either one. I've long felt that it's decades past going to a 4 day week (without 10 hour days) and it just stays around due to inertia. It would balance the week out more as 4/3 instead of 5/2.
That said I doubt it will take off. Even if you got a company to do it, that means everyone is taking a pay cut because no company is going to pay 40 hours for 32, even if they should.