A/B Testing whole emails within engagement program

I'm trying to A/B test two different versions of an email within a nurture engagement program.

I've set it up using the "If Random Sample = 50" setup in the flow step of the batch send campaign. 

Would one email be in the Choice 1 option, with the other email as the default choice? (attached).

Or, is the way to do this to use no default choice, and instead, use:

- If Choice 1 = Random Sample 50

Email: version 1

- If Choice 2 = Random Sample 50

Email Version 2

Default choice is empty

Thanks!