I'm getting older, this is my 2nd gig in life, and I'll get straight to the point. What is less manual labor, tarping and un-tarping a flat bed load, or unloading a refrigerated load?
Tanker. Tanker is so easy that I had 3 days off last week and was happy to come back to work so I could get some rest.
When I asked an owner operator how much he liked tanks, he replied that he didn't miss his refer days where he often got a floor load of those chocolate bars that schools sell for fund raisers. He said hoses were much better than fingerprinting 10,000 cases of candy.
Another vote for tankers. Dry or liquid, it's probably the easiest on the body. If you get into cryo work it's also better paying.