I would say it's a bit more than just opinion right now, because .CO.IN has been around for years, and major developed sites are using that namespace. Also, most of the notable reported sales have been .CO.IN, so at this moment I see it having a distinct advantage over .IN.
On the other hand, .IN is still very new. It's shorter. It looks better to many people.
Eventually, it could become the dominant of the two, but CO.IN is the established presence.