I did a bunch of research myself last year and went with Lightning Source. Here’s a rundown of the key differences:
LS markets itself toward publishers, rather than authors — you need to have your own isbn, design, editing, etc, since they don’t offer any of these services. Your book will automatically show up on amazon US, international amazon sites, Barnes&noble.com, etc., and be available to libraries and book stores through the Ingram catalog (Ingram owns LS). The key advantage is that you can set your retail discount as little as 20% to these channels. (This will prevent brick and mortar stores from ordering your book, but in the vast majority of cases they weren’t going to anyway). At a 20% short discount, this means that if your book retails for $15, amazon takes $3, LS charges you around $5 to print it (depending on page count), and you make around $7 per book. If you have some sort of plan to get your book into retail outlets, you’re free to set your retailer discount higher. (For more information on LS and selling on amazon, I recommend Aaron Shepard’s “Aiming at Amazon”)
Createspace is owned by Amazon, and they do offer more services geared toward authors who are not as on top of the publishing game. They’re also much more user-friendly, since they actively market toward authors. Books automatically show up on Amazon US, but retail discount is set at a non-negotiable 55%. This means that if your book retails at $15, amazon will take $8.25, createspace will charge you around $5 to print it (depending on page count), and you’ll make around $3 per book. They also offer expanded distribution (international amazon sites, library catalogs, etc.) for an even higher retail discount.
I haven’t used Lulu myself, but my understanding is that their online cover design tools and tutorials are delightful. They charge more for printing that LS or CS, though, and books don’t show up for sale on other online retailers, only the Lulu store, making them a good option for hobbyists, but less so for people with loftier ambitions. I understand that it’s possible to utilize their deign tools and then take the finished product to another printer, FWIW.
Every other US Print-0n-Demand company (Outskirts, Xlibris, etc.) acts as a go-between from you to Lightning Source. They offer various packages for design, editing, marketing and so forth, then submit the book to LS for printing and distribution. Some offer better services and better deals than others, but if you plan to handle these things yourself, it’s worth doing the research to go straight to LS.