When it comes to New York City neighborhoods, there are hundreds and hundreds of them, spread out across 304.6 square miles in five boroughs. With such a selection, it’s hard to pick the “trendiest,” but if we were hard pressed to make a choice, we’d have to go with SoHo. Today the downtown neighborhood is well-known as a shopper’s haven, with hip boutiques and major chains lining the streets, but it wasn’t always so trendy. SoHo’s massive cast-iron buildings were once home to…