Depending on who you bank with it might be best to take Euros from a hole in the wall in the Algarve.

We usually take some Euro's with us then the hole in the wall.

You could take some sterling with you and change it there, I think the exchange rate is about the same as buying Euros at the best rate here.

If you change cash you always get a slightly lower rate here. Over and above that, it is much safer to bring a small amount of cash in Euros then use your card(s) to withdraw cash as and when you need it. Restaurant bills and big shops can also be paid for using your card.

That avoids the possible problems associated with carrying and keeping large amounts of cash about your person or your hotel room.