You can use .html, .htm, .asp, .php, etc as your URL file extension.I wanted to ask if search engines prefer one of these over others.Thanks in advance !
No There is no advantage if we use keyword in file extension.I saw a video clip of Matt cutts on this and he clearly said no.search engine wont give any importance for such file extension.
Preference in SEO terms for URL file extension?- Yes I believe on that. There are many of preference in SEO
As per my experience i can say that, there is no more importance of file extension but file name have importance in SEO friendly URL.....