I'd say get the original SnB. It's great for teaching basics. SnB Nation goes over the material from SnB, but in less detail. It does have a few extra techniques though. The Knitter's Handbook is primarily for designing, tracking, etc.
I learned to knit through a little scarf pamphlet, but the SnB book is my main reference resource when I don't know how/have forgotten how to do something.
I can vouch for learning from scratch with her books though - I went through three books on crochet before Happy Hooker came out, and I though I would never be able to crochet. I've had HH for one month, and I have completed 2 projects, am in the middle of 2 more projects, and have started designing a shrug. I think Debbie is a brilliant teacher.