This question really has no answer and everyone will have an opinion. I asked myself this same question a few months ago, and it really came down to money. I would first set your budget and then look for trucks in that range. Everyone knows a diesel is king of towing, but they also can cost double what a comprable gas truck would.
For me, I coudn't afford a diesel without 200k+ miles, and even though the motor can go forever, other components, especially suspension and steering would be wearing out real soon, and need to be replaced. I ultimately went with my Dodge V10 gasser, it only has 105k on it, and it was in my price range. Does gas mileage suck, yes it does; but there are always trade offs.
OK, in short, if you have $10k to spend on a truck, get a mid to late 90s dodge or ford diesel.