I prefer online articles over books. Online articles are like quick recipe. You get what you want in a couple of mins. For webmaster Resources, I think you should include Scripts like submission scripts or tools like WebCEO. They are good and helpful tools.
You can get information online lately, but it is still better for a one on one lecture with someone who has experience on the subject. I learn easily if things were shown to me while it is being taught to me.
I think the best resource you can have are books, but the internet is more up to date so I guess you can go with both. Just try to be meticulous in finding answers to your questions and you will never go wrong.