I find this odd. While I’ve read more Adams than Pratchett, Pratchett–to me at least–is by far the more polished all-around writer. Adams would good through about Life, The Universe, and Everything, then gets really repetive and tedious. It took me ages to finish Mostly Harmless, but the first two books were classics.
Pratchett, on the other hand, only starts hitting his stride by the fourth book. I’ve read random selections from there, but they’ve all been well plotted, full of wry observation, and endearing characters. Also, Pratchett’s Discworld framework allows him much more room for exploring different ideas and characters.
They’re very different writers, in my opinion, but Pratchett seems to have more depth to his writing than Adams. Sometimes when I read Adams, I feel like I’m being pummeled with the same jokes over and over again. They’re good jokes, to be sure, but by the fourth book, I grow weary of the style and the characters. Pratchett is certainly more varied.
I probably like HHTG better than anything Pratchett has ever written, but overall, I find Pratchett more consistent and polished.