It's not really a mater of "good" or "bad", I look at it more as "right tool for the job." If you're outputting HTML, use an HTML doctype. If your document requires features of XHTML - extending the DDT, etc. - use XHTML. So the answer for most of us is likely yes, an HTML doctype is fine.
My interest was in reaching mobile viewers. The Wikipedia article on XHTML gives the impression that HTML 5 is now the interoperability horse that W3C is betting on. This supports g1smd's comment.
The article also reports that "Simon Pieters researched the XML-compliance of mobile browsers and concluded 'the claim that XHTML would be needed for mobile devices is simply a myth'". I will keep my eye on HTML 5.