I have a 1995 Jeep Grand Cherokee Larado and I heard that using super is a better alternative than regular unleaded, due to the fact that there is more ethanol in today's fuels.
This this question could also be more general to "older" engines as well.
You would most likely have to measure your MPGs with one, then the other. Some people have more success than others using Premium. I stick to Regular with 6 ounces of marvel mystery oil at each fill up to keep things clean, I get the best MPGs with that method.