I am fuge fan of MB4, but when I compared with other billing systems, WHMCS looks better for shared/reseller hosting service..
As I use MB4, it is great on billing part and server intergration(automation).. and I think that's all what shared/reseller hosting service providers are needed... expect that MB4 has some fraud protection modules, rich CC modules and ordering system..
however, when I checked WHMCS, it had what I needed and what MB has... I don't see much different..
I have not used WHMCS yet and it is not that old as MB, so I can not tell how is it inside of it...
it will be good and nice if you can share your expericen about WHMCS.. and
if you can tell reason that you used MB and move to WHMCS
if you can tell reason that you used WHMCS and move to MB...