I don't think there is any "perfect portal", but this is the one I've been using the last few months anyway: https://msrc.microsoft.com/update-guide
Because it lets me filter and sort in different ways. Because @Work people ask me for details differently, like "what was released for office in October" or "I just need to know about CVE-xxx-xxx stuff".
I happily send them off to that link for them to do their own research. :)