We recently hired a car with Alamo at LAX and plumped through prebooking for the smallest and cheapest. On arrival they wanted us to trade up to a bigger car (apparently a Focus not being a family car).
When we got outside to choose a car there were only huge cars anyway, so there's no point in paying for the upgrade. There were also lots of Prius sitting there as midsize cars but, because the European families were scared of the unknown, went unpicked. Read up on them before you go if you want a trendy midsize car.
Updates
Go for the Prius - it is just an eco car so will save you gas and the environment! I rented a car with a 'Rent-a-Wreck' style company. There are a few that buy ex-rental cars from the big chains and rent them out at less than half the price you'd expect to pay at a major chain. They aren't wrecks but do show signs of wear and tear (dents, scratches or even a bonnet that didn't start its life on that particular car). I think the company I used was called 99rent. Friendly people and no quibbles either picking up or returning the car.
Is this your business?