Well, if you are using only blog commenting for link building then you can use them because blog commenting is very effective if done in the right way.

For finding blogs type this term in Google:

"powered by Wordpress" + "your keywords" + "top commentators"

You would get great list of forums, you need to do quality commenting on these blogs and they would be approved faster as there are also other commentators on those blogs thats why you have to use top commentators in the search.