That depends very much on the location of your winter home. Public transport in the Algarve is good and there are good and affordable transfer services and taxis. Having said that, bear in mind that the Algarve is a large province with many rural areas. If you want to profit fully from the biodiversity and see all the beautiful areas, mountains, beaches and so on, having a car is really the best. But of course you can opt for renting a car now and then during your stay. In winter, rental prices are very moderate.