Working with Proxmox again. I like the ZFS integration now. I do not love the community support though.
exactly

.....
community support is lacking, but....
since proxmox uses unmodified linux kvm (and OVS), having linux knowledge is useful.
I am on proxmox 3.4:
*) tested zfs on command line, piece of cake. ZoL 0.6.3.X is stable on my purpose.
*) back to the drawing board, since I have only 24M RAM, and ZFS take some M byte RAM ( I can limit maximum ram limit). I just install hardware RAID 1,
overall is acceptable for me, but... community support is not good. I trust my linux skills mostly.
try openvz (tight to host kernel) and ditch out due to my purposes some VMs connecting to wild wild Internet and easy moving KVM image to another baremetal or backup.
do not forget to pick virtio when creating a VM, this is a beast fast for guest OS as long as modules/drives are loaded.