OOOh fun question: Here is my take on it. First off I am licensed in NY as a real estate agent - I am born and bred in a Manhattan co-op, and am still a life long NYC resident. That being said, the hottest seller continues to be 1BR and Studio Apts, they never stay on the shelves long. For many reasons, 1 - cheapest entry into Manhattan, 2 - easy to rent, 3- many young people are not married and do not foresee kids asap, so it is a perfect buy. NYC is a very popular destination for people coming to "live in the city" from all over the world. This lends itself to a constant demand for affordable property, and the stuido/1BR fits the bill.
Your question has some other facets which complicate the issue. I would say condos and lofts are more popular than coops, but the sheer volume of coops lends to more sales of coops. The consumer prefers condos due to their less restrictive ownership rules, although that also seems to be changing.
Buyers are coming from everywhere, we are more than a U.S. destination, we are a world destination. So eastern europeans are the fastest group coming into the city in general, and for the outer boroughs as well. The caribbean community continues to flourish as every other community does too. It's not like we are Phoenix - who goes there? i dunno... NYC attracts from all over the U.S.
Buyers do expect higher grade in new construction. Granite, Vikings, built in appliances, Sub-Zero, etc are expected in any new unit as are hardwood floors. Again, NYC is not a "new" city - many of our buildings were built long ago, so renovations are frequent. Brownstones are better if they are original, but that also depends on the buyer. Hope this helps.