The temperature in which you proof sourdough, not only affects how long you need to ferment it for, but it also affects how well the yeasts and bacteria consume the sugars and in which proportions. This also affects flavor.
Considering the balance you are looking for between fermentation time, efficiency, and flavor preference, it boils down to 2 questions: 1. How long do you want to ferment for? 2. What kind of flavor would you like?
Sourdough ferments well between 70F – 85F (21C – 30C), but it also has a pretty wide range of temperatures it can ferment in. Dough is pretty hardy and can take a wide range of temperatures.
There are 2 aspects that you can control when it comes to temperature of proofing sourdough. 1. Dough Temperature 2. Proofing Environment