Create A Forum - Support Forums

I have two questions:
(1)   In order to point a subdomain to a forum on CreateaForum.com, it seems there are 2 options, either through Cname or A Record.  Which option is better? I am somewhat more in favor of Cname because it does not involve specifying IP address. The IP may change, but the forum’s address (such as XYZclub. CreateaForum.com) does not change.

(2)   Where should we create a new record (either through Cname or A Record ) of the subdomain? At the web site of the domain registrar’s or at the web host of the main site, where the main domain name is hosted.

Thanks for your prompt reply.

I think Cname or A Record has to be done where the domain name servers are hosted, not necessarily the domain registrar.