I mainly use XHTML simply because it's something people ask for. When I finish my portfolio up, it might actually take advantage of XML.
If you look at most sites using XHTML, they serve the document up as text/html, so they're obviously not benefiting from the extensibility of XML. It might also slow down the browser a bit, since XML parsers in browsers are probably more lightweight than SGML HTML parsers.
Up until news of HTML 5, there might have been more advantages to XHTML, as it's what the W3C had replaced the future of HTML with. They were going to [pretty much] leave HTML and just work on XHTML for standard markup.
But the differences, with the exception of XML in XHTML, are fairly small.
And with regards to proper coding since it's been brought up, unclosed elements in HTML will pass through SGML parsers absolutely fine, in the same way that XML parsers will pass all elements closed through. For instance, if the browser sees <p>, then another <p> without closing the previous one, it already knows that you shouldn't be nesting paragraphs inside each other, because it's not semantic, so it starts a new paragraph. So getting into "good coding" practises need not always mean coding HTML to XHTML standards.
Choose which languages for preference. If you want XML, XHTML is your choice