Regardless of any perceived pros and cons comparing the two standards, in real world terms NAB is the North American standard and IEC is the European standard equalization for half-track mastering decks.
IEC tape played back on a NAB machine is going to sound all wrong and visa versa. NAB is the most common in the United States, Canada and Japan by far. New half-track Machines destined for the US were factory set for NAB EQ unless requested otherwise. Most US and Canada studios use/used NAB EQ.
While most mastering facilities that still accept tape should be able to accommodate either standard, some may not and there are other things to consider. If you want to playback other people’s tapes or your own older tapes you’re out of luck, unless your deck has a simple switch to change EQ. Most decks require changing internal jumpers, switches or adding internal components… resistors, caps etc, and recalibration after the change. Even some Otari Machines, which have an external NAB/IEC switch need internal tweaking for the repro side of things.
IMO there are no compelling reasons to use IEC on a half-track unless you live in the UK, Europe or Australia. It’s all about standards for the region you live in. Before the Internet you just didn’t see debates over these EQ curves. It was never about which was better. They aren’t competing standards, but simply and accidentally different EQ curves that were adopted as standards over time in their regions of origin.
