Why not read both?  They're both classics anyone who likes SF should read.  Do skip all later Dune books though.  The later Foundation titles weren't that bad, but I'd stop at the first set by Asimov and leave it there.

Then start reading Philip K Dick and get hardcore.

Oh come on, you really didn't like God Emperor? I find this hard to believe

Of the original 6, God Emperor is probably my least favorite, which is not to say that i dislike it, but i like all the others more...

I didn't dislike it, but Messiah, God Emperor, etc. really all felt weak next to Dune for me.  It just felt like Herbert had bottled lightning once with Dune, could muster a decent story, etc. afterwards but simply couldn't match the heights of the first title.

These days I tend to the view that you really might as well just read Dune and leave it there, perfectly poised.

Heretics! Heretics and malcontents! I am surrounded, besieged on all sides!

Dune, probably the best Scifi book ever written.

Although both series are good to book 3 then quickly become garbage.