The official BusTime app is great if you have a couple of "favorite" bus stops that you want to save for quick reference, but otherwise I find it takes way too many steps to get any useful information.

When I'm out and about my preferred bus app is BusBus NYC. The app opens directly into a simple map that shows all the buses in an area at once. It may be iOS only, though.

There are also some simple standalone apps that have the subway and bus maps. There's a subway map called KickMap Lite that I find easier to read than the official subway map.