City of Thieves was always my favorite, but Forest of Doom and Scorpion Swamp were my second favorite.
City of Thieves is fantastic and probably way more influential on fantasy RPGs than it's given credit for. (I think Americans generally overlook that these books were created by the founders of Games Workshop.)
Those two outdoor adventures are relatively easy, but a lot of fun, and good precursors to modern point crawls. Forest of Doom really feels like a BD&D adventure, much more than TSR's Endless Quest books ever managed to do.
The Dungeoncrawling ones were frustrating. I've never understood why The Warlock of Firetop Mountain is considered a classic. I read it once and then threw it in a box in disgust, never to pick it up again. As a middle-schooler in 1984 or so.
A big problem with the book, in my opinion, is that Ian Livingstone and Steve Jackson split it between them (I believe the hand-off comes at the underground river). Livingston's half is mostly wandering around a goblin and orc-held section of the dungeon (with terrible security!) and there's a decent amount of combat but no real puzzles.
Once you cross the river, combats become fewer, but much harder, and there's a "puzzle" aspect to the rooms that has a lot in common with early computer adventure games' "pixel bitching," where there's no way to beat certain encounters or get to the final treasure if you didn't know to make certain turns in the dungeon to find keys or pick up certain items. It's not great adventure design, honestly. Jackson's books in the line are generally pretty punitive and require you to replay them repeatedly to beat them.
That said, this dungeon has a ton of iconic encounters drawn by Russ Nicholson, who's best known to Americans for his drawings in the Fiend Folio. Warlock of Firetop Mountain, more than any Fighting Fantasy books other than the Sorcery! series, has a real dreamlike vibe to it that helps me, at least, overlook its flaws.
I've adapted the Advanced Fighting Fantasy version of it as a Shadowdark adventure and I really feel it holds up, even today. It's not as brilliant as City of Thieves or Deathtrap Dungeon or the Sorcery! adventures, but I absolutely see why it's the book they return to, in reprints, sequels and adaptations, time and again.
for some reason is my favourite one that really sticks in my memory for it's evocative writing and pictures.
