ModernBill is the best billing software, provide good support and services, easy to use and has number of features. It is a complete client management solution.
Never tried WhmCs, but i have to say I would never change from Modernbill. Easy to set up and use. Easy to integrate and the support is good too.
I am also using WHMCS with out any issues. Especially their support is good and they have dedicated support team for technical issues. So, that's why i preferred WHMCS.
WHMCS - much more user friendly and some of the modifications make it even more powerful from an administrators point of view.
WHMCS is certainly the best billing application for all the hosting providers as it has a lot of features and is very easy to use for the web hosting providers as well their customers. Also, it is very easy to setup rules in WHMCS which makes it even better.
I suggest WHMCS Really the best. take a look at this website http://www.unstoppablehost.com. Its totally on WHMCS
ABSOLUTELY NOT. They MAY have been back 3 years ago - I've been a heavy user of MB and its been nothing but trouble for the last 1.5 years - its stopped working - it hasn't been generating invoices - thousands lost - and absolutely 0 .. absolutely 0 support. I have JUST started using WHMCS - its easier to get acquainted but at the same time its going to be hell trying to get everything to migrate - I may give up. I absolutely hate MB.
WHMCS is an extremely powerful billing software once you get acquainted with all of the features. I've been using it for about seven months now and I am still learning new things about it.