CreateSpace has an advantage in that, for signing up with a special program with them for $39, you can order copies of your own book at a DRASTICALLY reduced price to sell at cons and such. Definitely a plus. They are also owned by Amazon, so I'm guaranteed to get an Amazon listing through them. Lulu can be a bit hit and miss in that regard.
So, what does Lulu have to offer? First, I'm already familiar with them. Second, they offer hardcovers. Call me a snob if you wish, but I prefer hard covers. The only question is if the hard covers make the books cost prohibitive. If they do, then that little nicety goes away. But Lulu still has the edge.
One thing I've been considering is ebooks. People like them, even if I'm not that thrilled with them. The problem with CreateSpace is their ebook creation process makes things that apparently only run on the Kindle, Amazon's ebook reader. With Lulu, I can make a .pdf without any DRM, so people can read it on their computers or phones or laptops or anywhere there is a .pdf reader. It also would let them back up the book, so that, if the unit fries, they aren't out the money they paid for it. Digital rights are a major consideration for me, and everything tied to a Kindle just doesn't seem fair to me.
Still doing research, still considering options. But with the approach to ebooks, Lulu has taken the lead.