Just some thoughts from this native Chattanoogan.
The two very best trains ever from Altanta to Florida were the Dixie Flagler(Chicago, Evansville, Nashville,Chattanooga,Atlanta, Jacksonville,Miami) re-named the Dixieland in Dec. 1954. It was discontinued Nov. 1957. That left the old Dxiie Flyer, described several posts ago by George Harris.
The other top notch train was the winter version of the Royal Palm, called the New Royal Palm. It ran Detroit (and Cleveland, Buffao, Chicago through cars) to Cincinnati, Lexington, Chattanooga,Atlanta, Macon, Jack, Miami.
There were other trains, as aptly decribed by George Harris--I am just pointing out my "personal best".
Chattanooga does still indeed have much, much long distance freight on several main lines. Today's NS was the former Southern RR. Today's CSX was the former Louisville and Nashville. Before that, in 1957, it had been the Nashville, Chattanooga and St. Louis RR.
The station still standing in Chattanooga, now known as the Chattanooga Choo Choo, was the former Terminal Station of the Southern Railroad. Trains went to Knoxville, Washington, NYC, Miami, Birmingham, New Orleans, Detorit,Memphis.etc,etc. There was another station. the Union Station, now destroyed. Trains there went priimarily to CHicago , Nashville, Evansville and St. Louis or to Atlanta and Florida points. Those were the L&N trains, (originally NC&StL).
There is a nice model train display upstairs at the Choo Choo Hotel which models both stations which used to exist in Chattanooga. Some of the equipment is accurate but some is not, inasmuch as it shows some Amtrak superliners. Amtrak never served Chattanooga at all.
As Alan pointed out the railroad cars are sold as unit space of one half a railcar. In no way corresponding to what we would call roomettes and bedrooms today. The ancestry of the cars is widespread and various. Some were lightweight, some were heavyweight. They were not all sleepers, indeed some were New York Central coaches, but extensively rebult It is not that far-fetched to have Nw York Central equipment in CHA since the Royal Palm, New Royal Palm and Ponce de Leon interacted with NYC above Cincinnati to such places as Detroit, Cleveland, etc.
I doubt that any of the cars at the Choo Choo were 10-6 sleepers. 10-6 came to be well known today since that is mostly what Amtrak inherited. But there were many other designs as well. So far as I recall, all 10-6's were lightweight streamlined cars; no heavyweight.
Speaking of Chattanooga having two downtown stations, let it be said that Atlatna had two downtown stations at one time as well. About eight railroads served those two stations.
The original question was just about Atlanta to Florida travel. That is a big enough deal. But Chicago to Florida was an even bigger, a separate matter by itself. As there were trains which did not go through either Atlanta or Chattanooga.
Oh yes, the train Amtrak inherited, the South Wind, went Chicago,Indy, Louisville, Nashville, Birmingham,Montgomery Jacksonville and Miami. Not Atlanta or Chattanooga. Shortly after acquiring the South Wind, Amtrak re-named it the Floridian andit was discontinued in 1979. While some of its route changed around, nothing changed at the southern end, such as to make it go through Atlanta.