using software would surely result in bad results. there is no substitute for human intelligence. most do follow blogs are moderated. anyone with an iq over 10 can spot a bot reply
I suggest scrapebox, love the spinning possibilities, and you can also comment manually using it... Havent used the other ones though, they might be better...
Manual commenting is the best approach, as if you are using softwares to spam hundreds of thousand sites, you'll finally get caught by Google, which will actually harm your site's reputation and ranking. However, you do need to find some software to help you identify dofollow blogs in relevant niches. Currently, I haven't found a free software yet. I'm looking to get some recommendation as well.
I think doing it manually is best way. At least i had never used this kind of software neither i would like to recommend.