My 2 cents ... Dont think it is a question of either one or the other. Think it is important to get vCenter statistics of performance of VMs because that defines which VM is consuming resources. It is equally important to look at the guest VMs and see which applications or processes can be causing this. see this interesting link:
Particularly for VDI, i think knowing what is happening inside the windows guest VMs is fairly important.
Regards,
Simon L.