Hello,
I notice that most hosting companies chose to tell you that WHMCS is better. This is also right in my opinion, although it's not just rather it has the most features or the most popular. You have to think about every aspect other than your own.
When a client who is at another company using WHMCS comes to your hosting company expecting everything to be better and they see that you both use the exact same billing system as the one they switched, then they might have second thoughts.
I belive that a customer wants to feel secure and like they are with a one of a kind host rather than one that is just like every other hosting company out there.
Best Regards,