Interfaces are the first generation of data flow software, Connectors are the second generation, with adapters being the third generation, effectively. What is recommended is dependent on your use-case. There is still a ton of usage of interfaces because there are no equivalent connectors or adapters for the same data source. Connectors are also just introducing high availability, which for some customers is required and has prevented them from using them.
I've seen some customers with good and bad luck with connectors, and they've made the decision that they're either going to use them or not use them based on their findings / testing. If you have an environment with > 50ms of latency between the data source and the data archive nodes, then you'll want a connector as ICU (and interface startup) is going to be slow due to some internal issues with the software & the interfaces.
