Search this Algarve forum. This matter has been debated incessantly.
Be aware that because of the economic crisis car hire companies in Portugal and Spain have substantially reduced their fleets this summer so there are fewer cars available and prices have gone up.
You may already find it hard to find what you want at the price you want.
In terms of best offer/service with pick up from Faro airport have a look at:
Luzcar - www.luzcar.com - Prices are slightly higher than others but are all inclusive and include 2nd driver and travel to Spain as far as Seville.
I have used them for at least 10 years.
Auto Jardim - www.autocarhire.net
Well established local car hire company with offices throughout throughout the Algarve and Portugal.
Yorcar - www.carhireyes.com/carhirealgarve/
Well established local car hire company.
All of the above are reputable established local companies.
