I don't have any personal experience with AdvancedMD. We looked into using them ourselves several years back but we find with most cloud based systems that the charge is way more than we are looking to pay. As a billing service with over 50 providers, it doesn't make sense for us to pay per provider.
We use Lytec which is server based, but they do offer a cloud version. They charge per seat so it's not per provider. I can send you the name of a reseller if you'd like.
Sorry I can't be more help!