Blog commenting and classifieds submission are both just ways of creating links yourself, and as I’ve already mentioned, these are viewed as worthless by search engines. If the sites are reputable, then those links will be marked as nofollow; sites which don’t follow this recommendation are likely to be regarded as participating in link schemes, and listing your site there might do more harm than good.
Blog commenting when you have something of genuine interest to add to a discussion might increase traffic, but posting just to display a link is unlikely to attract anyone.