I've pondered the Ford Ranger and Nissan Frontier but I figure that if I am going to get a truck, I might as well get a 1/2 ton. It didn't seem to me like they used enough less fuel to make them worth while. Not sure though - I will keep an open mind.
I used to have a '99 F150 supercab with the 4.3L six cylinder. I only kept it about a year and a half and only put a little over 12k miles on it during that time (it had nearly 50k on it when I bought it). But since I keep spreadsheets and complete records on my vehicles, I know that it averaged 18.114 mpg with a mix of city and highway driving, and I do believe in using the air-conditioner.
I now have an '01 Ranger supercab with the 4.0L six cylinder (for those who don't already know it, the Ranger comes with a 4 cylinder engine, a 3.0L six and the 4.0L six). I bought it with 36k on it and it just now rolled over 60k. All power and air and automatic, 2WD, and by far mostly city driving now, and it has averaged 18.554 mpg (slightly better than the F150). I do have the load distributing hitch platform and I made a few 65 mile round trips with a 17' aluminum bass boat with a 50hp engine and I made a few 30 mile round trips with a 4' x 8' trailer with a little ZTR mower on it. I think it's only rated to pull 5,500 pounds.
So . . ., as I see it,
1) the F150 will pull a heavier trailer, if you need that,
2) the Ranger will get a little better gas mileage,
3) the Ranger is just the right height for me to sit down or stand up from the driver's seat, while I had to step up a bit to get into the F150,
4) the Ranger, being smaller, takes less space in the garage and is perhaps a little handier parking in parking lots, and
5) the F150 rides a little smoother. The Ranger has a good suspension for hauling a pretty good load, but that makes it a little rough riding. I have hauled all the limbs I could pile on, even standing on a ladder, to the landfill after pruning trees and that was only enough load to make the ride smoother. But when I hauled over 1,300 pounds of concrete stepping stones, that was actually a little too much. I didn't have any problems with it, but it lowered the back end considerably, and I only had to go about 10 miles at 35 mph in town.