Which is the fastest way to load backups? (USB vs SATA vs ps3netsrv & ISO vs JB)

So I wanted to know which is the fastest way to play backups, how does ps3netsrv compare to an external USB drive and to the internal drive or even a 3.5" drive connected to the internal SATA port via eSATA (with 7200rpm)? I won't count SSDs since they are way too expensive for me.

I've read that it's better to store and load the backups as ISOs, this should make a difference if you store them on a USB drive or the internal drive, but does this also apply to the ps3netsrv?

I have an...

Which is the fastest way to load backups? (USB vs SATA vs ps3netsrv & ISO vs JB)