Simple. The third way you try, always.

USB-C is better than A in that it works in two orientations instead of one, but the correct answer for connectors should be any orientation — the best connectors are cylindrical connectors: barrel plugs, RCA, BNC, banana, phono, TRS, TRRS, etc. Just make them round.

The side with the holes. That's true for 95% of devices, with one of the few major exceptions being cheap chinese powerbanks

PS/2, which USB all but replaced, solved this by visually keying one side of the connector as flat.

Where the logo is.

The other way

It's very weird that USB-C solved the problem of "we can't tell which way to insert the plug" by mandating that both orientations should work, as opposed to just making the exterior of the plug as asymmetrical as the interior.