I don't remember having a milkshake, it certainly happened when I was little and I probably chose chocolate then. Now I would prefer coffee, orange, or blueberry.
Cookies and cream/oreos! I’ve had strawberry, chocolate etc milkshakes but none of them best the classic oreos for me. Pretty much always my dessert when I see a restaurant has one.
My favorite is mint chocolate chip, with the caveat that I've also had ones that weren't great because the mint was too overpowering. Typically, though, that would be my go-to at a place that has them; otherwise, I'll generally do vanilla or chocolate with little preference between them.
My favourite would be the peanut butter milkshake, but I've only been able to get it at this one restaurant that's whole thing is milkshakes. My second favourite would most likely be vanilla, and then oreo
My favorite is strawberry, followed by chocolate. There is a place a half hour away or so that has amazing strawberry shakes, and I always make sure to grab one there if I happen to be in the area!