I too would suggest reading in general order of publication, but not worrying too much about it as many should stand alone well. They read blazingly fast as well.
I recalled having enjoyed Rincewind and Twoflower so much in the first two books, but in making appearances later was unenthused. Went back and reread Color of Magic, and Light Fantastic again and they didn't hold the same impact for me that got me hooked. Odd.
The witches worked well for me for several books but wore thin. Death is also best used sparingly. He held his own as central character for a couple of books quite satisfyingly, but I think his appearances need to be kept minimal to maintain his appeal and interest. He's starting to feel overused to me as the witches did.
The Watch as core characters seem to have held up best and longest but the setting as a whole seems to want to fleshing out more. A little too much concentration on Ank-Morpork is not well-advised IMO. But, that won't ever keep me away from ANYTHING Discworld.