@Betty Xin welcome to BP. Hudson County and Bergen County (areas along the hudson rivers ) are great places to explore. The tenant quality is good. It is easy to find a family with stable income. I work and invest in Hudson County. Multi family houses are quite old here. A lot of them were built in 1930s or before. There are newer options. Houses built after 2000 are great for first time home buyer, with low maintenance but relatively more expensive. When you start looking, you will see the differences.
in terms of appreciation, I think Hudson county has great potential, but keep in mind most areas has appreciated a lot since 2012. Depending on the location, Jersey City downtown and Greenville have very different growth rate. Just to give you some idea, I bought a two family house in west new york in 2015, the price has gone up 30%~40% since then.
In my opinion, Multi-family are more desirable. It is easy to convert a two family house into one but not the other way around.