What would be the best approach for SEO where you have a domain (premium .net framework model) hosted on say server A, and you create another site (free PHP/wordpress model) to drive traffic to it. Would you host the latter as a subfolder or subdomain? Also, where would you choose to host the subdomain or subfolder, on server A or elsewhere?
Great Question! As I'm sure many other SEO's here have mentioned.. you should absolutely be leveraging the sub-folder as opposed to the sub-domain as Google and Bing associate sub domains as separate entities with their own value metrics outside of the primary root.
The only real time I would recommend a sub-domain over a sub-directory would be due to platform restrictions (Shopify, Wix, etc) where you don't have access to build an infrastructure to support nested content from multiple hosts.
Definitely worth chatting about, however you shouldn't have any problems using the sub folder with any other host you'd like.
I would always choose sub-folders over sub-domains. For the most part, sub-domains are treated as separate websites (not entirely, but for the most part), and sub-folders are treated as part the main site. Links to internal pages tend to pass more weight than links to external sites.
Subfolder is definitely the way to go. Here is why:
With subfolder, you share SEO juice with the root level domain.
If you do sub-domain, it's like a whole new domain (in the eyes of Google) and will not get any existing SEO benefit.
Subfolder all the way. There have been numerous tests done on this question, and they all show that the subfolder option gives you the benefit of the main domain. When you create a subdomain, search engines look at that as a whole other site, and you do not get the same benefit from being associated with the main domain.