Between HTML4/XHTML and HTML 5 I personally enjoy HTML 5 more. For one thing the tags that are used instead of divs make more sense and are easier to understand and have a more logical organization. Divs work great, but the tags used in HTML5 are just simpler to understand to me, and with divs the organization isn’t as clear when looking at the code.
I also really like the nav and aside tags. In HTML4 you would use an unordered list to create a nav bar, and then you would have to use extra styling in CSS in order for it to go horizontal and not have the bullet points from the list. In HTML5 you just the links under the nav tag and they are automatically horizontal and they automatically have no bullet points, and the less time I spend adjusting minor things in CSS the more time I can spend making everything else work. I also think the aside tage is a great idea, since in HTML 4 I tried to make one using divs, and ti was very difficult and temperamental. The aside tag in HTML5 is still not the most perfect solution, but it is easier to use, and it requires much less coding in CSS. I guess that for me is one of the biggest draws for HTML 5, is that I don’t spend so much time in the CSS code tying to sort everything out.