In the city, whether you decide to rent or buy an apartment is more a financial decision, based on your available resources and life plans. If you decide to rent, there’s a reasonable selection of attractive rentals (OK, reasonable by NYC supply and demand standards). If you decide to buy, there’s a good selection of apartments for sale to choose from as well.
The second home situation, at least upstate, is different. There’s a lot of demand for full-season summer rentals, but very limited supply. Most houses here in Sullivan County with second home appeal are owned-occupied, not investor owned (unlike the Long Island and Jersey shore areas, where there is a good supply of investor-owned rental properties.) There is a growing number of short term “AirBnB” rentals, but they’re largely owner-occupied houses that the owners are looking to rent to pull in a little extra income when they’re not going to be using them.
I’d venture that there are at least a few hundred people, if not more, looking for full season summer lake, cabin or country house rentals. But in any given year, there may only be a few dozen available. There isn’t a selection of hundreds to meet demand. Because of the short rental season here (unlike further north near ski areas, where there’s both a summer and winter season) and relatively low rental rates, there isn’t a lot of interest in pure investor plays for summer rentals.