The best truck for you will be the one that fits your needs and has been well cared for by its previous owner. Trucks can get some hard use, so the condition is more important than the brand. Trucks do not get good fuel economy because they are geared for work, not economy. Still, there are some things to look for to get better fuel economy. On a full-size truck, a V-6 will get slightly better mileage than a V-8, but it will be less powerful and not as capable towing & hauling. Most extended cab full-size American trucks have v-8s. The rear axle ratio has a lot to do with fuel economy. People who want to tow or haul look for 3.73 or 4.10 ratios (GM) or the equivalent approximations for Ford & Dodge. These will pull much better, but at lower fuel economy. For max mileage, look for a truck with a ratio of 3.08 or 3.42 or thereabouts with other makes - but keep in mind that they will not be optimal for hauling & towing. Most of the foreign trucks are sold with no option to get the best rear diff for the buyer's intended purpose. I've owned full size and compact trucks back as far as model year 1965 and the very best truck I have owned was a 2001 Chevy 1500 Z-71 ExtCab 4x4 with 3.73 rear. But it only got 16 mpg and I traded it in when my commute increased to 110 miles/day.
Will you need 4x4? If so, there goes your fuel economy. But if you need it, then you need it, and the lower fuel economy is a consequence of that choice. Don't buy a truck that has been used to tow heavy loads or 5th wheels etc.
American trucks of that age have better locking rears or limited slip rear diffs as optional equipment or part of an options package. Some Japanese trucks of 5-10 years age are very hard to find with this highly useful (I'd say essential) feature and some - like the first year Tundra couldn't get it even as an option. I had to pull one of those out of the local boat ramp with my truck.
Are roads heavily salted where you will be driving or shopping? If so, you should probably avoid Toyotas as they have had some of the worst rust problems for trucks 5-10 years old.
There are some older guys who baby their trucks and these would be the best candidates for purchase. Have your mechanic check it out BEFORE you buy.
Pickup trucks are all body-on-frame rear-drive, so the drivetrains are easier to work on than modern cars with transverse engines squeezed into small engine bays. There's plenty of room underneath to slide under there and work. Oil changes are simple. The electronics are no different than cars. There's just more room all the way around to work on a truck.
I like full size Chevy and Ford pickups best - but I would not consider them to be fuel efficient. If you are driving less than 12 or 15K miles per year, the added cost of gas doesn't amount to much. Insurance is fairly cheap, so the total cost of ownership should be more important than just one factor like fuel economy.