I recently rented from Hertz at SNN. If you're not dead-set on an automatic but think it may be nice, ask to upgrade at the counter. You may find they offer you an upgrade for far less than the res price.

On another note, Hertz wanted to charge an EU 25 fee for declining their CDW and using a credit card. They offerred there own for EU 4/day. BUT, it had an EU1200 deductable - not at all the same as a CC. I ended up taking the CDW from hertz.