Being able to pull it is not the issue, being able to stop is what you should be thinking about. I would never tow with a Ford Ranger, I also have a 2 horse bumper pull. I once pulled it around town with my Toyota Tacoma which is larger then the Ford Ranger. My Tacoma is used everyday for lawncare as well, I tow a utility trailer with two commercial mowers, all my other equipment, and loaded up with grass, branches and other things. But it doesn't compare to the weight of a 2 horse trailer with horses in it. The horse trailer will pull your truck around corners because the wheelbase will be similar, and the stopping power of your Ford Ranger is what will put you in real danger. It is a no brainer to me, if you have access to the F150, use it! Bigger is always better when towing, and in this case it is better to spend the extra few bucks if any that you would save on gas.
When you are sitting a top a horse, you are that much closer to God.