About HostBill being more graphical and features rich than WHMCS... I looked at their features and it seems pretty similar. And then I looked at the panel demo....
WHMCS is more feature rich and more graphical in my opinion for admins. Maybe a bit less pleasent on customer area, but that's easily customizable, really.
WHMCS has always been a standard and I believe they got the best development team. (probably because they are so popular and get more revenue
It's pretty clean and simple even with the tons of features it boast.