I have succesfully used Drivalia (2 mins off airport) 3 times in the past year and have booked again for next week. I have always done so via
www.doyouspain.com. I simply choose the options I want on the left hand side of their results web page and always plump for fuel full/full. It is hassle free as long as you have a credit card to put a hold deposit on their insurance, A good cheap car excess insurance policy from your own country and the ability to give them a firm "no, I don't want your daily excess insurance policy" (astronomical costs).
The amount of people I see everytime i've been there who have paid 25€ or less for one week car hire and arguing over the fuel & insurance policy's when they get stung is astonishing. Do your homework and you'll be fine.
When I booked car hire for late January 2016 I did so in November 2015 - At that time the price for hire of a Fiat 500 was approx 9 cents a day or around 15 cents for a Ford Focus. 63 cents for one weeks car hire surely sets off alarm bells. I eventually booked a Fiat 500L for 60€+ (came to £46.52 GBP) full/full and additional driver free - nothing more to pay other than fuel top up before I return car.
Current prices for March/April are very high. I'm looking to book last week in March 2016.