I had a couple of diesels in the past, and they most certainly tow wonderfully....cannot be beat. I have also towed with a v10, which towed almost as good, but cost more in fuel at the time.
Today diesel around here costs $.50 a gallon more than gas.
So, it depends on what you tow and how often and where.
In July, I bought a new Ram 3/4 ton. Drove both diesels and gas, and opted for the hemi gas engine. The rational was that I only tow about five time a year, mostly lesst than 300 miles. We usually take one or maybe two major trips of up to 1,200 miles or so. I live in Illinois, which is pretty flat, and most of the places we typicall go are relatively flat....planning a trip ti northern Wisconson in July which is mostly pretty flat.
Also, the truck is my daily driver, and I really dont need a diesel to go 14 miles to work.
We are thinking about going to Arizona next year...I know it will be an issue towing 8,000 pounds through the mountains, but to buy a diesel for one trip seems silly to me. While I wont like running 4000+ rpms at 45 mph up hill, but, again, for a one time shot I can deal with it. If we decide to do it quite often, I am certain the local Ram dealer will be glad to sell me a new Ram...hahaha
Anyway, for now my hemi suits me fine....no DEF to deal with, cheaper fuel costs, now fuel filters to change, no fuel additives to deal with, cheaper oil changes, and I get about 18-19 mpg hiway unloaded.....same or better than some diesels.