Often overlooked is what else do you plan on using the truck for?
If dedicated (or nearly dedicated) to towing, I would recommend the 250/2500 or 350/3500 for a TT over 7000lbs GVWR.
If you are using the truck as daily driver and need the additional fuel economy and better ride, then perhaps a 150/1500 would be a better choice (if the payload and towing specs were met).
I enjoy towing with my GMC 2500HD but only drive it once or twice a week other than towing.. If I had to commute in it daily, I might have looked at the 150/1500 trucks that can handle my trailer..
It is really personal preference, the forum is telling you that there are many variables and you need to decide what is important for you.