Blog commenting is the way of leisure if you are the one who wish to make a natural comment but for the real link builders, they will try hard and do everything to get bunch of backlinks so they are not think directory submission or blog commenting. What they want is backlinks pointing to their sites.
You should be doing both and also don't forget article submission. (among other things) These r great for developing anchor text relevant back links. i'm also using article, and directory submission.
I find that directory submission is almost close to useless and shouldn't waste time on it. Just go for blog commenting, a proven easy and fast way to build backlinks.