As stated this is a very personalized topic.
This link show the size of truck most people are pulling with.
This topic is another sensitive one but needs to be researched about weights.
Another discussion about the vehicles. I think this one has the best evaluation of current vehicles
There are a few members out here towing with Gas and they can give you their opinion.
Mine is if I was buying new (spending the big dollars again) I would go Diesel and a big MDT or HDT converted unit. Again just my opinion.
Best of luck, cheers,