It depends on what you want. A light boat could be towed by something as light as a Ranger or F150 pretty easily.

It also depends on which type of diesel engine truck you're looking for.

The older 7.3L engines don't have as much power as the newer ones, but are widely regarded to have better fuel economy and less problems. The newer 6.0L and 6.4L engines get worse fuel economy and have been known to have their issues, but are very powerful.

Any diesel truck is going to cost much more to maintain, it's just the nature of the beast.

I'd recommend an F150 for your use. The better retained resale value of a diesel is offset by the increased maintenance cost, and gas SDs really drink a lot of fuel no matter which one you get. An F150 would get reasonable MPGs and provide plenty of towing power for your boat.