For a DB, iscsi all day long. At work we have some of the fastest storage available on the market today (SCM drives in front of E1.L super fast SSD all connected with 100gbe mellanox switches and NICs) and it barely can keep up with the MySQL DB. NFS would absolutely work for the other use cases. But these are enterprise class systems for an entire university so yeah lots of load.
For a home system, I’m not sure it matters if the load isn’t much. I prefer iscsi because I know how it works. I use it for VMware datastores even at home. Anything that is shared storage between webservers or the like, NFS is almost required since shared iscsi storage is going to be very difficult to set up outside of something like VMware datastores since the file system is setup for multi-writers. Other filesystems like Redhat’s GFS2 or Oracle’s OCFS can do it but it’s not cheap or easy.
Tl;dr summary: my suggestion is iscsi for the DB and NFS for the other stuff.