For production environments this depends on the storage.
For a lab - especially since you are using both option in production - I'd consider to setup both, iSCSI as well as NFS storage, if you have sufficient resources available.
If resources are low, I'd probable install the NFS role on an existing the Windows server (which I assume you have in your lab). This can be done even on a domain controller.
Actually, because I'm on a budget, i have a box loaded with CentOS 7 to create my ISCSI Targets (using Targetcli). I figured I would save money and learn more about Linux at the same time.
I just wanted to put this question out there to see what everybody else is using as far as their datastores in vSphere. Either one works great!
I'm going to go out on a limb and say that NFS is a little better due to the fact that you can still write to it at the source level (on the SAN). ISCSI is pretty much a one-way street.
Anybody what to comment on that? I would love to hear it.