Do you prefer using pure HTML 5 in creating a website from scratch? Why or why not?

Html5 comes handy when you want to use features that is not in html4 or in older version like 

The canvas element for drawing

The video and audio elements for media playback (No requirement of plug-in)

Better support for local offline storage

New content specific elements, like article, footer, header, nav, section

New form controls, like calendar, date, time, email, url, search

So Html5/CSS3 combination eliminate of using most of JavaScript, images and third party plug-in requirement.

Using pure htlm5 depend upon your requirement but I personally go with progressive enhancement method considering browser compatibility specially older browser & some version of IE doesn’t support most of html5 features so I would recommend progressive enhancement & graceful degrading approach when using html5.

well, it depends, HTML5 & CSS3 are the main trned these days for markup languages, the new tags included in HTML5 such as (video, canvas,article,section ... ets) help you a lot to construct a very easy to read structre for the page, then as answer for this question, yes i definitely will use HTML5 :)

Welll i certainly will use html5 in my website creation but  of course u will need to use with it like framework php or asp or depend on your requirements

but if your website is only static data with no database ( or small database using indexeddb for example )and with using some animation  it will be great to use html5 in this case

Just note that any website you built, you can use the html5/css3  technology   coz it contain the new tag elements as  type phone , numeric , calendar .....