Which one/Who is stronger?

[Exalted Father]

Are they both grammatically accepted when talking about human?
*Which one is stronger? or who is stronger?

 

[emsr2d2]

Are they both the following sentences grammatically accepted correct when talking about humans?

1. Which one is stronger? or
2. Who is stronger?

Note my changes above and that I have changed your thread title to include the complete sentence you're asking us about.
When you give us more than one option or sentence to look at, please number them.

There are instances in which either one would work but if you use "who", you can't go wrong.