[kevindong]

From a simplicity perspective, I'd prefer a text message with a 6-10 character numeric code that can be auto filled with one tap.

Aka the Lyft model (they probably didn't come up with it, but they're the main example that I can think of off the top of my head).

[MobileVet]

Sure... text is fine but easier to hack typically. For low sensitivity, it is probably faster than email.