I would echo what thorpej2 has said. The queues for goldcar are often long and on my last visit they were massive!
I've booked through a number of companies now and would also echo what others have said.
Full/Empty - this type of rental expects you to pay for the full tank of petrol (50-60 euros) plus an admin fee (approx 20 euros). Any unused petrol should be refunded.
Full/Full - car has a full tank and return full. No fuel charge, no admin fee. Usually only available if you take out their insurance.
Insurance - a huge rip off. Better to take out your own and pay excess and reclaim if there is damage. Can be done on an individual hire basis or take out a yearly policy if you travel often. Will require you to provide a guarantee of the excess though nothing will actually be charged unless there is damage.
Good companies I have had: Inter rent at Alicante. Great prices, no pressure to take their insurance, fuel charge taken at end of hire i.e. no full charge then refund. Good overall service nice car (Kia Picanto) air con worked.
OK companies I have had: Europcar at Alicante. High Prices, high insurance costs but good overall service. Nice car (Volkswagen polo) but aircon didn't work
Poor companies I have had: Dickmanns at San Javier. Good prices but lots of pressure to take their insurance. Full fuel charge taken on hire and refund on return. Poor overall service, bad car (Fiat Panda), dirty, very small and aircon didn't work
To date I booked via EasyJet for Europcar, good service but pricey. I booked the other two via DoYouSpain who offer the excess insurance.
Just watch out for the hidden extras in the T&Cs and just refuse the high pressure sales tactics on the insurance and take out your own excess insurance. Be prepared for a circa 20€ charge on the full/empty policy