Hosted ITSP Setup Recommendations

We are a small ITSP, that is looking to go to a hosted setup for our customers. Currently we have 2 Asterisk based trunk servers in different geographic regions and have been deploying a server at our client sites connected via IAX2. We are planning to co-lo a new blade system that can easily be expanded as needed.

My main question is in regards to what would be the best setup for the hosted solution, and why? I am considering two options…first is to run a virtual server per client, second is to run a multi tenant setup. Both setups will be run on ProxMox or similar hypervisor configured for HA fail over, and connect to our existing trunk servers via IAX2. We are trying to keep the cost of the solution to a minimum, but are open to paid solutions.