Cost-wise, the best approach is to have 2 IS/TN instances in a cluster (for failover purposes) in one location and have all locations use that one site.
However, other factors may push you to a distributed approach. Again, those factors are driven by what integrations will be hosted by the infrastructure, the service levels needed, anticipated volume, etc.
I’m not sure you’re going to get meaningful recommendations on which approach to use without providing more info about what the characteristics of the integrations.
#webMethods#Integration-Server-and-ESB#B2B-Integration