Hello, I just think which works better from SEO point of view..Totally separate domain name with keywords like abc.com or abc.abc.com ? which is better ??
Offcourse a seprate domain will be the best but if u have a high traffic sites its better u make a sub domain to extend it
No doubt separete domain is always recommended but to it take lot of affort to market all the domain. So you can use it as sub domain also.