Is blog commending working? Sort of. It works, but doesn't work great. It's good for getting pages indexed, for link diversity, and for minor SERP boosts. Is it good for ranking a keyword #1? Not really, at least not without being supported by other methods.
Please follow below mentioned steps to find a niche related blog for commenting:
1: Find Where Your Target Audience Is Already Going
2. How Active Is The Blog?
3. Is The Blog Already Creating Great Content?
4: Competitor’s Backlink Analysis
5: Blog Submission Websites
6: Search Query Method – (Google Search Parameters)