Best truck

It depends on the truck and depends on the person driving it. If you buy an older truck with the expectation of working on it regularly and are capable of doing most of the work yourself then you have potential to do really well.
If you put a doofus behind the wheel of any truck it can put you under. The newer trucks defuel or derate and have automatic transmissions and abs systems to curb the damage inflicted by the user. The same systems that prevent damage are also more maintenance than an older trucks basic needs.
If a person does a thorough inspection on an old rig they stand to end up with a very profitable truck in my opinion. On the other hand, they could go broke in the first month from catastrophic failures.
I'm just more of a gambler and absolutely despise these drive by wire trucks so I'm biased towards buying old and keeping them running.
I'm currently running an 87 peterbilt with an old mechanical engine and it's biggest drawback is the fuel consumption. It cost me a fraction of the cost of buying a newer truck and I haven't been late for a single appointment since I started running it. It's paid for, theres zero payments and it earns me the same paycheck that I would be earning if I were in a modern truck with a hefty monthy payment and increased insurance rates. It doesn't have the space, gadgets or cruise control that the newer trucks have but it still brings home the same rate per mile. It works for me because I'm willing to work on it.
It's not for everyone but I highly recommend running "seasoned" equipment.