Regular or high test gasoline

High test gasoline is for high compression engines that "ping" or predetonate when using low octane gas. "High test" or premium has more octane which slows down the rate of the explosion. Actually it has a little less power produced, not that you would notice it, but it won't help millage.
That said gas with ethanol has less power also. In that case the premium (if it dosen't have ethanol) could result in better milage.
Is it worth the extra money? Not usually.

Use regular. If you want to save gas (not sure why it matters right now since gas is virtually free) you just need to slow down.

Your Ford manual will tell you to use regular gas and I suspect has an 87 octane requirement. There are those that will say that "X" brand of gas is better than Cheapo's. Don't know. Call Ford if you want there current specs.

Most gasolines come from the same pump at the refinery. The guy that delivers to a Chevron station, according to what I was told, carries a container of techron to put in the tank.

The latest generation of digitally controlled engines can better compensate for fuel quality, but years ago I drove 1984 Volvo, what was 1st generation of digital engine management.
The engine was design for regural, but with 112HP it was struggling on long grades we have in CA.
So for annual trips to Las Vegas I was fueling with Premium.
Thanks to that instead of redlining on lower gear, the engine would pull the grades on overdrive.
I did not do it for fuel saving, but for time saving, but strongly believe that avoiding downshifting saved fuel as well.
Maybe not to degree to make it worth spending extra money, but to consider.

I only use what truck manual recomends..87 regular in my case,,fuel up at PetroCanada stations as much as possible as it contains some kind of Tactrol(sp)
Aditive that cleans the engine,,have been very satisfied with this for many years..

I tracked mileage on my 27' Class C with a Ford V10 on various brands of gasoline for several years. I consistently got better mileage using top brand names like Shell, Sunoco and Exon. I could never get the same mileage using discount brands like Murphy, etc. I will admit if you take the price difference into account with the mileage, it might work out about the same overall cost.

My Ford V10 never pinged on anything, but octane doesn't seem to affect mileage.

So, what's different about discount brands. Not sure - maybe the fuel is older? I know gasoline has a short life, as far as top efficiency. Some say there's no difference and even come out of the same delivery truck - yeah, right. All I know is my tracking showed there is a definite difference.

Or maybe the discount brands are more likely to have ethanol. Ethanol will definitely lower mileage. Just about any brand, even top brands, come with and without ethanol. It's up to the distributor/station which to sell. Most states require a sticker on the pump, but they have a way of disappearing.

Best bet for top mileage is to buy top name brands without ethanol - if you can find it or even care anymore...

In most US fuel terminals all gasoline starts the same. If it will be Shell it gets the Shell addatives....if Mobil/Exxon it gets their package etc. The V10 was designed to use 87 octane....use it as you will not increase mileage using premium.

If you Google this subject, there are no less than 15 web sites which have written about this subject. Every one of them come to the same conclusion, stay with the gas your vehicle is designed for. Using premium gas makes no difference, except it may cost, maybe, a dime more per gallon.

Use what the manufacturers recommend. If they say 87 octane, then use it. As far as comparing mileage of different brands, those figures can vary even if you use the same brand of fuel.
If you look at the pump next time you buy gas, read what the "ethanol" sticker says. It usually says something like "UP TO 10% ethanol. This means that it may have 2%, 5%, 8% or 10% ethanol. The actual amount will vary and the more ethanol that is in that particular station's tank on that day the lower your mileage will be. Come back next week to the same station and the amount of ethanol may be less, who knows?