I dont think it matters a huge amount. Many people do the latter these days so there might be some preference there. But to be fair sometimes you see 2 subfolder before the post url title which can help if you have a large volume of posts across topics.
Personally I prefer the former (with single sub-folder) as 1) rather than 'blog' I'll use words that suit overall site article SEO purposes and 2) it works nicely with analytics to grab all posts in one sub-folder for build analysis.
Overall I dont think it has a huge impact.