SEO URLs html or directory?

Would it be better to have a URL like
"blah.tld/free_cellphone_ringtones/"

or
"blah.tld/free_cellphone_ringtones.html"

or a hybrid way like
"blah.tld/free/cellphone_ringtones.html"
"blah.tld/cellphone/free_ringtones.html"

I have seen some sites switching to the ".html" from the directory way and was just wondering.

"blah.tld/free_cellphone_ringtones.html" from my personal experience. The higher the level, the better.

Thanks a bunch.