Don’t know about the best 3 hour cut per se but having a quick look around fanedit.org I’d say this version sounds like it could be my definitive version of Dune once I get a chance to download and watch it.
https://ifdb.fanedit.org/dune-the-alternative-edition-redux/
Hadn’t thought about a Dune fan edit till now thanks to your thread and it is one movie that definitely needs some fixing. I’ve actually been looking out for the theatrical release on DVD for ages as the 3hr version is absolute rubbish despite the extra footage. Seems though that I won’t need to now though 😃
.Val