A standard Ranger is set at about 1250 lbs. payload (and "payload" includes the people in the cab. Remember that. It's the same for any pick-up truck).
Any of their drivetrain combos should be able to handle that load.
You'll obviously have to shift down more often with the 4 cylinder, but it will still handle the load.
For general "household" work, I've found the 4 cylinder / 5-speed manual works just fine. Sure, there are times I wish I had the 3.73 or 4.10 rear end, but the 3.45 does just fine 99% of the time.
...also, a couple of years ago, I found an added bonus to the taller rear end. I was dumping some cut branches in the woods and while pulling out, I snagged on a large branch and got stuck in the soft dirt. I just kept puttin' the coals to it, even shifting to 2nd (possibly 3rd) and the truck finally got out.
What I realized was that if this were my old truck (which used the same size tires but shorter 3.91 gears), I probably wouldn't have been able to get out, because the taller rear end gave me increased wheel speed without overrevving the engine too much.
As much as I cuss them, that's a chalk-one-up for the 3.45's.
Granted, my Ranger is a '98, so it would use a different engine, but I understand those Duratec engines had tons of torque (they should, considering how undersquare those engines are) and were long on reliability.
Can you tow a small trailer? Depends on the rear end gears. AFAIK, all of the Ranger's with 3.45 gears were not spec'd with a tongue weight because it was suggested they not do any towing....however, if you can swap in one of the shorter gear sets, I don't see why you couldn't tow a small trailer with the 4...especially if you're pairing it with an auto trans.
Dean