The first few books aren’t considered as good because Terry’s concept of the Discworld, as well as his writing style, hadn’t been fully solidified yet.
If you’d like to read them in published order as closely as you can while still getting good writing, I’d suggest starting with Pyramids or Guards! Guards! If you’re not terribly concerned with reading them in order (and truthfully, the way Pratchett structures his stories, it’s not actually a requirement for most of the books), then Small Gods is an excellent introduction to the setting. Hogfather is also an excellent one-off.
More generally, stick to the novels between 7 and 20 of this list and you’ll get a feel for the setting and characters. I find it’s better to have a fondness for the characters already in place before going back and reading the early stuff so you can mentally adjust for the writing. Most stuff after 20 is more ‘advanced’, and is better helped by having a good understanding of the setting already in place (except for the Tiffany Aching series, so I’m told, but I haven’t read those). That’s all just my opinion, of course, and probably more overly analytical than you’re really looking for.