You really have to think about your traffic patterns as well as the capabilities of the device doing the load balancing. Most devices default to some sort of destination mac address and/or IP address. That is great in most situations, but not if you have a port channel to a NAS devices. All the destinations will be the same, so your distribution won't be very good. That means the switch facing the NAS would want to load balance based on source. The NAS would want to load balance based on destination. It just depends on the use case.