How to choose best wordpress plugins for your blog?

The first thing I recommend you do is to identify your needs and from there find and select right plugins for your blog. There are some essential plugins that any WordPress blogs needs such as SEO, Contact Form 7, Akismet, the security,..etc. The others choose you based on your design requirements, marketing, social networking and other categories.
When you are going to install a plugin, make sure that it's quality and is well developed in all aspects. To do this you can review the comments through search engines, see how many downloads it has and try it for a few days.
If a plugin has few negative comments and downloads, better not using and seeking an alternative.

which plugins your blog is using? what are your ways on how to choose best wordpress plugins for it?

It depends on your requirements for running a blog or an ecommerce site. If you run your blog for business purpose then I would use wooeCommerce plugin for better selling and manage shop carts. If you run a blog for writing articles and sharing to everyone, maybe SEO by yoast is a good choice for your blog.