Well, this is a mighty 'heated' topic, ha ha. Generally the range is 78/82, but keeping a relatively constant temp is considered the most critical. However, if you keep certain animals, like catalina gobies, you have to look at the lower range, perhaps even 76 or so.
Here is a classic article, that has resulted in some debate, but it gives you an idea at least Dr. Ron Shimek's Natural Reef Temps and Salinities
I think that constant temperature is the key. If you choose 75 or 82, keep it as constant as possible. Temperature fluctuations are more problem causing than any specific temperature.