It's a hard enough choice that I've decided to eat both at once.
I'll untwist the oreo and stick a half to each side of my chips ahoy cookie.
You won't believe the awesome (and neither will I)...
Though if we're not talking about the "oreo" brand, but the classic "single-stuf" oreo, the choice is easy. Chips Ahoy (w/ milk).
If we're talking any oreo, so that the deity known as "double-stuf" is a viable choice, then the vote probably sways back to oreo.