Huge single storage pool for lots of VMs, or seperate storage pools for each VM

Background

Two identical 2008 R2 servers for running VMs with Failover Cluster (Hyper-V)
One IOmega NAS (old) with 15 VMs sharing one large (2 TB) clustered storage pool
One VNXe NAS (New) Nothing setup yet

I am getting ready to start exporting all of my VMs from our old SAN to our new SAN.

Is it better to create one huge clustered storage pool that will be shared between all the VMs, or would it be better to create separate smaller clustered storage spaces for each VM?

Thanks,
Brian