With PanAm, I flew 707, 727 and 747 cargo airplanes rather frequently, and also by choice. As I was instructor in the training department, we often used selected cargo flights for initial line training of pilots and flight engineers. To mention also, the freighter aircraft we operated were often the "best" versions of the aircraft model, higher weights and more powerful engines.
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During a layoff from PanAm, I got the chance to fly DC8-63F and 73F, which were outstanding airplanes, plenty of power with the CFM-56 engine version.
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After PanAm bankruptcy in 1991, I flew a 6 month contract with Cargolux, which I consider a great cargo airline. With them, I flew their 747-271Cs, the last year they operated the 200s and were in the process of getting 400Fs, so they needed short term contract pilots while their crews were on training for the 400 planes.
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An amazing fact, the upper deck of the Cargolux 747-271C had 16 F class seats, as they could carry passengers, and in that case, would have a flight attendant on board... as an example, we flew Mercedes cars for the Dubai Car Show, and we had the VIPs of the Daimler-Benz on board being served champagne, and lobster... on the way to Dubai... top class service.
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I am now with Aerolineas Argentinas, we have leased 747 cargo airplanes at times, and I always requested these cargo flights. The culture with many passenger airlines, is that cargo pilots are in a "lower class" than those who fly passengers. That is the old legends of the pre-1970 years... Take FedEx or UPS pilots, who are enjoying higher salaries than pilots with numerous passenger airlines...
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I personally prefer cargo flights. As mentioned above and other places, more often "on time" than passenger flights, and no complaints from boxes. Flying for "passenger comfort" is sometimes reducing you bank for turns to 20º, whereas you really should do 30º bank as procedures require, but then, passengers think you fly acrobatics...
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One thing that should be mentioned of flying cargo, is the concern of "weight and balance", critical in a 747 cargo, which is not the case of 747 passenger airplanes. With passenger 747, if it fits in the plane, no matter where they sit, or the belly cargo is, nothing to worry about. In a 747 cargo airplane, an error could lead to disaster...
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Happy contrails