WHMCS can be modified highly.. HostBill is getting to be something, but its certainly not close to there yet.

Once you ever use WHMCS for 2-3 months, it's all over you'll be hooked for sure! Who wouldn't be hooked, using the best selling WHM billing system around. Almost 4 years for us, and its still being refined, enlarged and just plain better every free up-date.

WHMCS/cPanel Is definately the way to go. It is not the most popular Control Panel for nothing. This is very userfriendly and is constantly getting new updates and ad ins.

+ for WHMCS