It's a tough call, but if all things are equal, like age, wear, and tooling, I would go for the Logan. Like Mathewsx I also have a Seneca Falls machine with change gears. It's a 10" machine like the Logan, and it's served me well for over 20 years. Personally I believe the Logan is a better quality machine, and parts will be easier to source should they ever be needed.
Having a QCGB is nice, but certainly not mandatory. I think you'll find threading is something you won't be doing on a daily basis, so changing gears won't be a major inconvenience. One caveat would be to be sure ALL the change gears are included. If some are missing it could be a real PITA to make or find them.
As a side note I also have a Sheldon 13x56 lathe with a QCGB. Both machines get about an equal amount of use. The advantages of the Sheldon are a larger through hole in the spindle, higher available speeds ( the Seneca Falls machine is only capable of 650 rpm while the Sheldon can turn 2,200 rpm) , and obviously larger chuck sizes can be used. The ability to use larger chucks on the Sheldon machine is a bit of a mute point in that I only have 8" chucks for both machines. In the 20+ years I've had the Seneca Falls machine I can't remember a time when it was too small for the parts I needed to make. Similarly since the largest chuck I have for the Sheldon is an 8" I won't be making any larger parts with it either unless I purchase another chuck. I don't see needing a larger chuck a necessity at this time or any time in the foreseeable future.