Hello, thanks for your reply.
I don't have CPanel installed on the server, but I have access to the DNS records and Apache. It is currently setup so that all of the domains point to the same DocumentRoot, however this does not redirect the domain names, which is what I need.
If there is no difference in the effectiveness of both methods I think I would go for the CNAME approach, however I believe this is more of an alias than a redirect? How does this effect other things such as searching engine rankings?