Two books on HTML? Why? And which one do you read?
Head First HTML with CSS & XHTML was originally published in 2005 as a beginner’s book on HTML and CSS. It still is that. So if you’re completely new to HTML and CSS, and you want to learn these technologies from the ground up, start there. There is some discussion about doctypes and validation that is quickly becoming obsolete, and all that talk about XHTML 2.0 being the future is definitely obsolete. Otherwise, the book will give you a solid grounding in HTML and CSS, which is exactly what you need to read Head First HTML5.
We’ll be updating Head First HTML with CSS & XHTML later in the year, so look for a new edition, tentatively titled Head First HTML & CSS. In it, we’ll be covering the major new semantic elements that have been added to the language, as well as some exciting new CSS capabilities.