[ryanchants]

Multi-tenant is almost always my preference. Data can still be segregated per-client at that database level. Multi-tenancy with a solid session caching layer will allow you to horizontally scale as needed.

Multi-instance will require setting up new servers per client. Potentially increasing cognitive overhead of which servers are handling what. Definitely increasing costs, as each server will have idle CPU cycles that could have been used to serve up a smaller clients.