I posted this a while back on the WHMCS forum and my blog, and I think users here could benefit from my comparison as well.

Check it out:

http://sethcole.wordpress.com/2009/09/07/whmcs-vs-modernbill/

If you want the short version read below:

"Plesk Billing is terrible, there support is worse, and the automation is lacking. WHMCS is the superior billing software. In fact, the WHMCS Plesk module works better than the Plesk Billing Plesk module. UGH!"

If you are thinking about switching I highly recommend it. WHMCS even offers a cheap migration service.

I hope this helps someone, or should I say spares someone...from the Plesk Billing nightmare. :{

Well, certainly WHMCS is the industry standard for a reason. We still offer Plesk though for those clients comfortable with that package.

Plesk seems a little more fancy and a bit more nicer but whmcs can be like that too with better options in it.

WHMCS is the industry standard at this point, i recommend you use it, it does a fantastic job

Plesk Billing is very complicated and time consuming. I highly recommend everyone that owns a hosting company or a company to use WHMCS.