Can anyone tell me what the best automated billing software is for hosting?

There is no "best" software.

Read through here for a while and come to your own conclusion.

http://www.webhostingtalk.com/forumdisplay.php?s=&forumid=9

Modernbill has a good reputation- and is used by many hosts.

I'm not going to say my usual line in these situations :)

modernbill - for intermediate and advanced hosting users
WHMautopilot - average user. easy

Best one is Modernbill (www.modernbill.com) it's pretty advanced but has more features than other scripts in the same area.

Of course there others less advanced scripts.

intermediate and advanced hosting users

LinkPoint offers reliable merchant gateway software.

I tried ModernBill, but found it too big to actually use in a small project. I am now looking at AWBS, will let you know how I like it.

Also you can try clientexec or whoiscart :)