This is just my experience, so don't take it as the truth. That said:
I have not had a day of formal training in my life. Up until college started a few months ago, everything I knew was self-taught. If you think that's interesting, I also never bought a single book. I learned early on that Google is better than any library (in some senses). You can find a tutorial on just about anything on Google, as long as you look.
Now some people just can't follow something if it's not in a book. That is perfectly fine. If books work better for you, go for it. I just personally prefer to read a guide or a manual. Saves money, doesn't take up a lot of space, and I can carry a LOT more PDFs than I can books.
Where books come in handy is for things like the A+ or any other formal test. Any guide you find online might be great, but will most likely be outdated. In addition, I have yet to see one guide that contains all you need to know. You might need to read a guide on hard dicks, a guide on electricity, several books on Windows commands, etc.
I'd suggest the official CompTIA A+ study guide. That or the ExamCram book. Or A+ for Dummies (Shamefully, I got that one to study from). The A+ is basic, but I've heard it can be hard if you don't focus on details. As such, I'd suggest a good blend of straight book learning and online insight. I'm rambling, so I'll end with this: Do what works for you, and do it well.
EDIT: I went ahead and highlighted my typo for everyone. Enjoy the laughs at my expense =D