If the choice is these two, I'd take the Miata. They both are going to be an absolute riot to drive, but the Mazda is a lot more liveable on a daily basis. Better seats, more flexible powerband, better (and lockable) storage in the cabin. All these things matter when you own a car and get overlooked.
On the 2006, I really like it on a look/touch/feel basis (they only have one, so they aren't letting people drive them). It's the first MX-5 I can fit in with the top up.
