Since we spend a lot of time in Spain ourselves we know where to get the best prices for rental cars (we always rent a car when we're in Spain).
Here is the top 3 sites that we use to check availability and best prices. The prices changes, so sometime the Hispacar is cheapest, sometimes some of the other two. It's worth check prices.
To share with you the experience I have had together with the problems that there is with car hire at Malaga Airport, there are two things to be aware of:
My recommendations about Insurance is to either pay with a card that have an rent-a-car-Insurance and to accept the reservation/security deposit. Or to buy the Insurance locally (not the one
offered on the websites, since they are not connected to the rent-a-car-portals I have recommend above) and to see the rental price together with the Insurance (€12-25/day depending on car
category) as what it cost.