Which plan do you most enjoy doing and why?
For me it’s Gravity as I love the V02 max work…it’s fun, sufficiently challenging and the short intervals mean it feels like less of a grind. As a mtber whose comfort zone is definitely short punchy power, only 1 threshold a week and no sweet spot is a god sent.
Funnily though, I feel sweet spot base is what has the best effect for me. 
Favorite: The one I just finished.
Least Favorite: The one I am about to start
Serious face: I am approaching two years on TR and I have done a fair amount of variety with different base/build plans: SS, polarized, traditional. Too soon to say which has been the “best” for me.
I feel like the plan I am enjoying is really based on mood. This winter I experimented between traditional and polarized. I enjoyed the traditional block because it was “predictable” in terms of the effort I needed to give but it wasn’t much mental stimuli but it allowed me to adjust to many hours on a trainer. If I had to pick a favorite it would be polarized over SS or traditional. Seems to take the best of both worlds in terms of variety (between longer z2 rides and intervals) and volume.
I’ve only ever done 40km TT plans mainly because that what I do and it hasn’t harmed my endurance/ leisure riding (if anything its boosted it) and which I also I like to do. So with nothing to compare it too I can’t really say what my favourite/ least favourite is.