Games I remember liking the prep for…
Dungeon World: not all of the prep, but I loved, loved, loved putting together Fronts, evolving them out of the players’ actions. My favorite bit is when I put the Fronts down and aha suddenly I have a clear picture in my head of what the world and the campaign will be like.
Golden Sky Stories: getting to put together an emotionally-resonant human situation for the players to encounter was fantastic, and I definitely appreciate how you can more or less do stats on-the-fly, statting characters as per the general NPC guidelines.
TBZ: my one experience prepping for TBZ was doing half-baked scenario prep beforehand, and then hurriedly putting details down in order to make a coherent, interesting city with relationships between different bits of it.
Burning Wheel: when I burn up some really cool NPCs with neat backstory, and I finally “get” a character who hadn’t been statted up before, and who was previously in the background. I once spent a half-hour doing this on my commute, the NPC got wasted with a longbow the next session, and I didn’t even mind! I had a great time getting to know the character.
So I guess the one common thread here is: I like prep that helps me get acquainted with the world of the game, which resonates a lot with the statements about Dogs. That moment where the people and major players of the game come into sharp focus for me is magical, and any prep that contributes towards that (like drawing up factions, working out relationships between characters, or fleshing out pertinent world backstory) is something I like.
Stats are eh.