Hmmm...
First book: Color of Magic, though I didn't know it was in a series until much later.
Favorite book: Going Postal, the Truth, or Monstrous Regiment.
Favorite character(s): Moist von Lipwig (confidence tricksters just make my day), Adora Belle Dearheart (I don't know how a woman like her survived high school with that name. On the other hand, it would explain a lot of things...), Lord Vetinari (both the old Patrician and the young rebellious Assassin), Leonard of Quirm (Leonardo da Vinci in Discworld, hilarity ensues), DEATH, Cohen the Barbarian (the very very OLD barbarian), Twoflower the tourist, Rincewind the cowardly wizard, Archchancellor Ridcully, Granny Weatherwax, Nanna Ogg, Just about every character ever written into the Discworld universe I have loved equally. If Detritus were to force me to answer, he would have to kill me 'cause I honestly can't choose.