Just a thought, but what would happen if you do both? www.sub.example.com can also normally be accessed using www.example.com/sub/index.htm If you have external links from other sites to the subdomain and pagerank flowing from the main domain through internal links, do you think google would add both together, or consider the 1 page two different pages?
according to me both work well depends upon your site.. but in case of subdomain google treat it as different domain so i think it can get index well instead of deep link. some time crawl dont crawl very deep pages in that case we can use subdomains. and if you have site like shopping then always use subdomains for the products category
I think if you have your site and business relevant blog and it have good traffic then you can linterlink your site with it then i could be helpful for SERP, and if you have sub domain then it could be helpful for traffic not for SERP.
It cannot be good for your site, this is something I read somewhere along the way. But still need more confirmation as no reason was given.