Depends who you ask. Hopefully somebody who knows what is what!
Probably 南傳 which is the more common term. Especially for the living tradition.
上座部 (not 上坐部) includes all the Sthavira / Thera groups, including Sarvastivada.
It thus tends to have more of an historical sense, viz the 大眾部, for instance.
My recently moved Blog, containing some of my writings on the Buddha Dhamma, as well as a number of translations from classical Buddhist texts and modern authors, liturgy, etc.: .