I had heard about the series for ages before consuming any content. I have ADHD so I read pretty slow, and that tends to bias my enjoyment to visual media. I first watched the Colour of Magic and Light Fantastic mini series with Sean Astin, then Going Postal, and they were all great. I'm reading the books now in, I believe, publication order. Currently on Sourcery. They've all been quite enjoyable so far. Granny's headology still cracks me up.
The miniseries are a lot of fun! I rewatch the Hogfather miniseries every Christmas. I have heard the Watch on Amazon is terrible, and from what I have seen and heard of it, I'm inclined to agree. I also read them in publication order as well, though many people recommend against it. I quite enjoy the headology in all the witch books.
Yes. Publication order is definitely the best way to read the books. You get to see the world develop, You get to see Terry's skills develop. You get to follow Ridcully's and Stibbons' arcs in order. You get to spot all the crossovers and references of bigger events and minor characters.
But...
It can be a bit overwhelming for new readers if they're told that its a 41 book series, and the best character isn't introduced until book 8, and the best books start around book 19, and the first couple of books are in a bit of a different style to the later ones, and the best book is book 29.
So my generic suggestion is for new readers to pick up Guards! Guards! and then decide whether they're hooked enough to read the whole series in order, or want to carry on with the Watch books. If I know a bit more about the asker, I might suggest starting with a different one. If its winter, I'm likely to suggest Hogfather.