IMHO todays gas engine are plenty adequate for most towing applications, unlike 20 years ago when gas engines were pretty marginal for heavy towing.
So.... today gas vs diesel is a personal preference. As for the claims of high maint. costs etc. on diesels, my 2004.5 duramax that our son now has turned 250K miles. Other than oil changes, filter changes etc. the ONLY engine/transmission repair has been a new fuel filter seal kit.
We now have a 2015.5 duramax, only 60K miles but again very trouble free.
so pick what you want, not what others try to convince you of.