Which one first..... tough choice but i like the Star Wars reference. Question is though 'what would be commercially successful?'. I would love to see Guards Guards made into a movie but not Nightwatch. Or at least not until several movies have been made to establish the characters. Guards Guards would be great because it has a dragon in it and who doesn't want to see that !. But it remains a tough call. The star wars approach may be the best. Come in halfway when all the characters have been well established in the books and for that i am going to go with Feet of Clay. All the characters have good roles and i always enjoyed this novel. So that is my choice for taking a book and making it into a movie. That is, however, not what i would do if i was to make a city watch movie. I think it should be a standalone totally new story with much broader brush strokes in terms of character display. Same characters, same city but not an established novel. Realistically its the market that drives the story. To get the fan base outside of the original novels would have to be a driving factor. But here i would hate to see the star-wars approach. I loved the first 3 movies of star-wars but hated the last three (or the first 3 depending on how you look at it) because i had matured in the intervening years and wanted the movies to have matured. Unfortunately i got Jar jar binks
I would dearly love to see the Discworld novels made into movies. But i just don't see it happening. And i really dont mind that for two reasons. Harry Potter and Star Trek. Harry Potter because there is only so much you can put into a film. I love the Harry potter books (46 year old single male) but i always felt a little sad at what had been left out. I mention star trek because i dread it becoming a franchise and multiple series coming out. I cite for your perusal Deep space nine (shudder) Voyager (cringe and shudder) and Enterprise (cringe, shudder and squeeze into corner crying with shame and remorse). I want to see the books made into movies but i also don't. I wanted to see the voyages of G'kar made into a series as well. But i am glad they didn't. I wanted to see Garibaldi hunt down and kill Bester but i am glad it wasn't made into a series because there comes a point where you have to leave well enough alone. I cite Crusade (bursts into tears and hugs copies of B5 to chest, all the while softly whispering "Why, why").
All in all i will always watch any attempt to put Discworld onto the screen. And i will be glad that someone tries to do it justice. But to be honest, i prefer the books to stay as books.