People from Commvault I've spoken to, usually say "on the client".
This is more of a number issue; i.e. you have 500 servers, more or less equally distributing the load, versus 5 mediaagents, which should be doing the same hashing.
I personally think it depends on the hardware of your MA. If you have a couple of old SPARC's; DDUP on client. If you have quad-socket, quad-core MA's with 256GB of RAM, DDUP on your MA.
So; depends on your enviroment.
If it jams, force it.
If it breaks, it needed replacing anyway.