Best market for 4 - 20 unit A - B class apartment buildings?

[Alex Price]

I've fix and flipped 1 - 3 unit homes but now I'm turning my attention towards 4 - 20 unit apartment buildings in good areas. Would like to know what are best cities for investing in apartment buildings and where good deals can be found. Also what are things to look out for when looking to invest. Good advice is appreciated :)