I like prepping, like it less when I've neglected it and I'm rushing at the last minute, like it much less when I'm at a mental block and don't know where to go next, and
love it when *ahem* "a plan comes together."
I was at a total "campaign block" the other day, the massive, political-type conspiracy that looked so cool at the start of the campaign was just looking drier and drier, and I was fresh out of ideas. So I drew it out on paper, realized how much the PCs
didn't know, and scrapped the whole thing. So freeing, I can't even tell you, and now I'm on a roll. Good times.
NPC stat blocks (skills, especially, moreso for rogues and bards), not so much, but even those have their moments. And I
cannot get enough of dreaming up monster settlement populations, relationships with other settlements, dungeon ecologies, so on and so forth, to the point that I do it even when half of it won't end up getting used.
I know what's going on, and it makes it easier for me to run it so the PCs
want to know what's going on, in which case I've done my job as I see it.