The only F redemption I've done was with LH, flying FRA-PVG (pre-2.5x days) but agree 100% with the above. Wonderful experience from entering FCT to waking up after a long and comfortable sleep, and they staggered our breakfasts so we could take care of Little Miss Sofasurfer (then only 18 months) which meant I was eating bacon as we started our final descent - never had that outside of F

Having now done a few C redemptions (long-haul: AC, LH, OS, TP, JJ, SK) I think if you've never flown in a premium cabin, and sharing the experience with a significant other... if it's a choice between two long-haul trips in C and one in F, I'd suggest two more comfortable journeys will be more enjoyable and conducive to a better start to your trips.

But, as others have pointed out, if you're sitting on a stack of miles you'd prefer to use given the current situation, the F experience is certainly something to experience at least once in your lifetime!