Generally speaking, there are enough studios-to-1-bedrooms and 3-bedrooms-mega pads. However, there is a shortage of 2-bedrooms (both small and large). Small meaning 1000sf or less. These are ideal for an individual/couple who needs the second bedroom as a home office or are expecting. Large, meaning 1300-1800sf. Think two large bedrooms with a living/dining area. These are great for families with 2-kids (regardless if they are the same sex or not) or an individual/couple who have guests and like to entertain.
The greatest demand for these size spaces is in established neighborhoods. Ranging from the Upper West Side to the West Village to Cobble Hill. Perhaps a recent sale of mine explains it best... 708 Greeknwich Street #4D
(a 2-bedroom with home office, 2-bath, 1300sf) was on the market for 10-days and had 15 offers. The list was 1.9M and it went $300,000 over the asking price.