If I didn't have one already, I'd go for the ten-volume set. Seems a lot to pack into two volumes.
I have often reflected over the years how a great deal of the space is taken up with Crowley's stories, poetry and plays - which don't interest me personally, apart from the incomparable "The Testament of Magdalen Blair" - and that perhaps I should cash in and buy a copy of Gems instead. There's something compelling about the ten-volume set, though, and I'm happy to stick with it.
I'd definately supplement a set of the ten volumes with Vol III No 1, the Blue Equinox. With Crowley's Commentary on The Voice of the Silence, Achad's diary, and The Book of the Heart Girt with the Serpent, it's as good as any of the ten volumes.