Have you watched the TV series of the former? If you have, while the book is probably worth it the series is a massive spoiler and I think would mean that you may get more from Dune.
If not, then are you up for the whole series? If you are, I think the whole of The Song of Fire and Ice is significantly better than the whole Dune series, which gets "variable" shall we say.
If not, then I think Dune is the better stand alone book. It tells a story, and while there is plenty for the sequels to do they are not "required" in the way the rest of aSoFaI is.
When I was running part of my
King's Heir story past MaryKB for her feedback, she said that part of it reminded her of Game of Thrones (I'd created a couple of other kingdoms to go along with the one in the game this story is based on, and I'd upped the court intrigue and noble family interactions considerably, creating a few dozen new characters ranging from servants to monarchs, in all age groups, walks of life, and levels of education; of course some characters are secondary at best and some are tertiary, but the original game had far too few characters to make the story plausible as a prose adaptation). I do consider that a compliment as I'd never thought to be compared to a successful fantasy author. But I've never read the books and haven't seen the TV series and now I never can, until I finish my story. I don't want to be unduly influenced or accused of plagiarism.
Dune makes a satisfactory standalone novel. The protagonist succeeds and the villains are dealt with. The sequels that Frank Herbert wrote - Dune Messiah and Children of Dune complete Paul Atreides' part of the story, and that's the line where many Original Dune fans prefer to stop. God Emperor is a boring, miserable slogfest (unless you happen to love the character of Leto II, which I don't; I loathe him). Heretics and Chapterhouse feature Duncan Idaho (the one character who is present in all the FH-written Dune books).
My advice is to not waste even one nanosecond of your life reading anything by Kevin J. Anderson/Brian Herbert. It's all crap. I do recommend the
Dune Encyclopedia, which was compiled by Frank Herbert's friend, Dr. Willis McNelly, and it had FH's approval (with the caveat that future novels might not align with some of the Encyclopedia's content, which was fair; the Encyclopedia only goes as far as God Emperor, as it was published before Heretics and Chapterhouse were written).
For the love of god don't read the Dune sequels. Fantastic book, ignore the follow up unless you felt The Silmarillion was worth the time.
As mentioned, the first three books by Frank Herbert are okay. The rest... depends on your tolerance level for boring characters (Leto II) and weird Bene Gesserit characters.