grammaticality - Are all these prepositional phrases equally correct?

I'm trying to understand when to use classic compound prepositions. Is there any particular reason to prefer/avoid any of these patterns?

In what field could we put it where it wouldn't interfere with the existing code?

What field could we put it in where it wouldn't interfere with the existing code?

What field could we put it wherein it wouldn't interfere with the existing code?

Answer

All three are grammatical, but the last is archaic, or at least legalistic and exceptionally formal, and you might therefore want to avoid it for other than some special effect or other. Some people might not like the second one because of the stranded preposition. That's up to them, but there's nothing wrong with it.