Hey Gary,
I found a few pictures online since I don't have many comparison photos on my phone. In my opinion only, I prefer the lines of the Knick over the Flues.
You will have to decide which you prefer
I believe the earlier Flues may have had finer engraving versus later Flues, the transition to the early Knick was similar to later Flues, and then the latest Knick's had less engraving than the earlier Knick's. The last of the Knick's were produced in 1980.
This a fairly early 1917 Flues with finer checkering followed by a 1950-1960's Knick.