The 3/4 is a much better tow platform. As a DD they work great too. They ride rougher but compared to HD trucks from a few years back they're very comfortable. The biggest challenge as a DD may be height in terms of getting kids/wives in them and going into parking garages.
Half tons (just my opinion) are glorified crossovers. They get decent mileage and can be quick with the right motor, but they're mostly people haulers that can tow on occasion. The max tow ratings on them are a bad joke.
I'd recommend checking out the Cummins over the 6.4. It's a much more capable engine.
