hi goodluckdomain, when you will add a sub domain for your blog, it will be just like a new website and Google and other search engines will take it as a whole new and separate website. On the other hand if you use folder for your blog, it will be just a new directory on your website and it will be a part of your website. I will recommend you to go for a folder to run your blog. Thanks

You basically have to take it from your ultimate goal's perspective. What would you want to achieve with this sub-domain? Having it as subdomain will basically mean (in most dynamics) that you have another domain name. But yeah, see what you want to achieve first.

sub domain is recommended, because this is considered as the separate domain and links will also get more worth here

subdomain better , google tend to rank subdomains with keywords on it better than websites with keywords on the folder !