In Portuguese, how do I say?

In European Portuguese, how do I say I would like another beer? I have become friends with several Portuguese in the Algarve where I go every year and they all say queria mais uma. One waiter in the Algarve told me I should say quero mais uma. A Portuguese instructor at the University of Washington told me that queria is more formal thus more acceptable in Portugal if followed by a polite phrase like faz favor. Also, why wouldn't I say gostaria mais Uma?