I've seen them all (yes, even Revelations). My all-time favorite is Hellraiser V Inferno. That.. was INTENSE!
But another one I enjoyed was Hellraiser Hellworld. Now that was really interesting because the dude that played Superman in Man of Steel and Khary Payton aka Cyborg from the Teen Titans show (I BELIEVE he reprised the role for Injustice) were both in it, so I got alot of enjoyment out of watching Superman and Cyborg in a Hellraiser film.
I do intend to work my way through the franchise. I've seen all seven Saw films, so I can surely sit through all of Hellraiser.
If you haven't already, I'd recommend the original novella (The Hellbound Heart). Well-written, more graphic, and not restrained by the limitations of film making.
What's more, Barker has finally finished The Scarlet Gospels, which will return to the Cenobite universe (it's supposed to be Harry D'Amour VS Pinhead, which sounds sick).
What's more, Barker intends to remake/reboot Hellraiser himself, with Doug Bradley reprising his role as Pinhead. That could be very interesting.