That depends on who you ask. There are a number of technical issues with this question, which preclude a simple and short answer. In reality, the latest W3C recommendation with widespread support is HTML 4.01. Unless you actually need any of the features that XHTML offers over HTML, there is no technical reason to use XHTML.

In order to actually benefit from using XHTML, you really need to understand the fundamental differences between XHTML and HTML. Such a site will only be available to a small minority of the surfing population, however.

Some web designers and developers prefer XHTML's syntax rules over HTML's. By following certain guidelines, you can use this syntax without technically using XHTML at all (see below). There are a number of potential pitfalls with this approach, but it is a possible way forward for those who absolutely want to type <br /> instead of <br>.

For 'future-proofing' your documents, using a Strict doctype is more important than whether you use XHTML or HTML.