I think it boils down to: do you want an employee for "your" (singular) start-up, whom you will pay (at first) in shares, or do you want a co-founder for "your" (plural) start-up?
I think either choice is valid, if you can find the right person. But you should decide how much control you want to keep for yourself, and what that implies for the other person's motivation and initiative.
I think either choice is valid, if you can find the right person. But you should decide how much control you want to keep for yourself, and what that implies for the other person's motivation and initiative.