I find these topics great because there are just so many of them....
WHMCS; Everyones first choice. Then there are the others in which you have listed. These are all popular programs and yet everybody uses them.
Allot of people have not heard of Blesta... www.blesta.com
. On first site of that software it may not look to be the best software around. Uppon further investigation, it does basicaly everything that is needed from a billing system for a web hosting company.
I am suggesting blesta because it is not something that every hosting company uses, it's cheap, and it's stable and reliable.