From my point of view, you'll get better result if you put have links from relevant blogs. If your site's niche is health and you get a link from a Plumbing blog... I don't know how could that help you.
If you are trying to get good rankings in the SERPs, then NoFollow is a complete waste of time. If you want to still attract human readers by your blog comments, then you can still get some traffic by commenting on NoFollow blogs. It really will depend what your goals are, and how much time and money you have to work with.
I see nothing wrong with throwing up a comment on a no-follow blog within your niche. I mean if you took the time to visit the page and your about to comment you might as well finish what you started. You might even see a little trickle of traffic if you get lucky.
couldnt have said it better Ninja, I prefer to get a visitor who will return to my site because of the value I provide him then get a link that I dont even know if it would provide any positive outcome.
somepeople comment anywhere they go and even leave a link with an anchor textof their name which is not related to their website, and though , they say it works fine for them
Google not count 'not follow' as link but if you submit comment related to the niche it will get traffic. thanks