Read them all when I was very young. Can't exactl remember which I preferred. Only read the 'authentic' ones though. None of these modern retellings. Children and God Emperor were pretty good, solid reads I guess.
I read most of them, a long time ago. I only bothered to keep the first two (Dune and Messiah). Dune is absolutely outstanding, one of the all-time classics of SF, but the series as a whole is an object lesson in trying to stretch a great idea much too far.
Sadly, this is all too often the case. Series are extremely popular with publishers because, once readers are hooked on the first one, they are very likely to buy the rest. So if you want to persuade a publisher to take on your book, you'll be in a much stronger position if you can show that it will be the first of a series. The problem is that the authors run out of steam; very few can maintain high quality over a long series.
I think the first one is one of the best books I ever read. When I decided to look up the rest of the series I only got through half of the second one and somehow lost the interest. However, if that depended on me having to much school work to do or if it was just not as interesting as the first book, I cannot say...