Good question! There seems to be a ton of info here: bb.steelguitarforum.com/viewtopic.ph... I’m learning in E9, as my steel lives in E9, but I think any tuning with an easy ability to slide to minor chords.

Oh cool, thanks! Seems like there's no definitive answer which just makes it more fun. This is reminding me how badly I want a Fender Stringmaster.