The gas/diesel debate will go on forever, nothing will change that. All you can hope for is related personal experiences that hopefully match what you plan to do and are helpful in making your decision. I've owned both gas and diesel, they both have their place. I drive a 2008 2500HD for work and unloaded mileage is 16.7, but I do a lot of stop and go driving with a heavy foot. If I baby it, I've gotten about 18 mpg. My 2013 3500HD DRW in my sig line gets 13.0 mpg with a 5000lb. camper and averages better than 18.5 unloaded freeway mileage.
If you want a diesel, get a diesel as you'll never hear a diesel owner pulling a steep grade with a load saying "gee, I wish I had less torque and was getting poorer mileage". My .02 worth.