By classifying behaviors (rather than data values), behavioral types abstract structured protocols and enforce disciplined message-passing programs. Many different behavioral type theories have been proposed: they offer a rich landscape of models in which types delineate concurrency and communication. Unfortunately, studies on formal relations between these theories are incipient. This paper argues that clarifying the relative expressiveness of these type systems is a pressing challenge for formal techniques in distributed systems. We overview works that address this issue and discuss promising research avenues.