difference between Portal access resource and webtop links in full webtop

I'd say the easiest way to differentiate them is to say that Webtop links are generally just additional links to applications that don't require and special processing by APM (e.g. a link to google.com, or a company's public website), wheras the Portal Access Resources are associated with ACLs (e.g. allow/deny based on uri) and rewrite profiles (where the APM will rewrite content on the pages to proxy requests through the APM).

This link and this link may provide some more high level info.

Hope this helps.