If you are going to be towing, get the V6. Don't get me wrong, the 2.3 in the Ranger makes a nice little mpg ride, but it sucks at towing. I own a 2008 with the 2.3. The manual transmission is rated to tow about 1500lbs and the automatic about 2100. The automatic will not get the mileage the manual does. Therefore the difference between a similarly equipped V6 and 4 cylinder will be minimal.
A better choice would be the F150 with the 3.7 V6. I think the mileage rating is actually a little higher than the V6 Ranger.