In general, a director will have more scalability in terms of number and types of ports, protocols and interfaces (types of blades), overall performance, redundancy and perhaps partitioning or other advanced resiliency features. Avoid the temptation to replace several switches with a single director. Instead, for high availability, deploy a pair of directors as separate fabric and data access paths. They key is to identify what your needs and requirements are in terms of performance, protocols and interfaces, number of ports, topology and availability among others and align the applicable technology to meet those needs.
I'm sure Brocade, Cisco, McData and Qlogic would be more than happy to help educate you on their particularly switches, blade switch, stackable switches, directors and router products. You can also learn more about switches and directors including how and where to deploy them in Chapter 7 (Storage networking devices), Chapter 8 (Storage Network Design) and Chapter 9 (Storage Networking Topologies) of my book "Resilient Storage Networks" (Elsevier).
This was first published in October 2006