As milkman said, the MTB bug bites hard. You can take a true MTB change the tires and make a few adjustment and it makes a OK hybrid or park trail bike, if you decide to do some off road style riding, a hybrid doesn't work so well for that. Don't think because you are 57 you cant do the off road stuff, I ride with a couple guys in their mid 60s. Fisher back in the day was the bomb, but now they really are just a name on a trek bike. At the end of the day, you take a Trek with the same components and compare it to a Specialized it going to cost more, you pay for the name. At the level of bike you are looking at, all the frames will come from China / Taiwan and probably made in the same plant. I think the reason against Trek is you will get more bike for the buck with Specialized, GT ect.

Bottom line, find a couple of bikes that work in your budget, fit you and your son and go have fun. Everyone is different, no one in our family rides the same brand bike, each of us like the feel of a certain bikes more than others. I ride a Niner, my wife rides a Fisher, my son a GT, my daughter a Raleigh.