I think Monstrous Regiment was supposed to be a young adult entry? But I'm surprised you included Carpe Jugulum, when for me "making money" was by far the worst. it seemed so derivative, as if it had been generated with an LLM trained on his previous work (or maybe a ghost writer helping out a very sick pratchett..)
I admit there are a couple I've never read (they're sitting on the shelf next to me - Raising Steam, Unseen Academicals, Making Money). That way I'll always have another Terry Pratchett novel to read.
I felt that Carpe Jugulum was a retread of Lords & Ladies, and the formula was getting stale by that point.
If Monstrous Regiment is YA, it has to go up against Tiffany Aching, and it definitely loses there.
The funniest: Pyramids (The groan-inducing punchline about the brothers alone is worth the price of admission, and it's basically stand-alone!)
The best: Night Watch (Sam Vimes' moral anger in full glory).
Weakest: Either Monstruous Regiment or Carpe Jugulum.