but assuming you want the same technologies included in the vblock what would make to go to one route or another?
vBlock is a set architecture from VCE, which is a partnership between Cisco, EMC, and VMWare. You don't get to choose which vendors VCE supports in a vBlock. It's these three. You have latitude based on which switches and blades and storage shelves you get, but they're all coming from these three vendors and are supported by VCE.
vSpex, on the other hand, is a set of reference architectures that include components from other vendors such as HP. This is not supported by VCE. This is installed and (potentially) supported by larger VARs that partner with EMC. VSPEX is entirely EMC-driven.
I understand that vspex is flexible (not bound to single vendors) but assuming you want the same technologies included in the vblock what would make to go to one route or another?
If you build a "VSPEX" architecture out of EMC, Cisco, and VMware and don't buy it as a vBlock, then there's no advantage. What you're doing is buying the three separately and you don't get to leverage unified VCE support.
This is a good read on the difference, and why VSPEX came about: http://www.virtualizationpractice.com/emc-vspex-vs-vblock-or-netapp-flexpod-can-vmware-vars-refuse-the-offer-15560/