I use very often meshes and curves, because I know what they are used for (meshes for renders and curves for follow curves). But I actually don't use surfaces and metaballs. What are surfaces and metaballs used for?
I can't speak for metaballs, but surfaces are the geometry you would use before computers could handle smoothing polygon models. The idea of a nurbs surface is that you have a number of isoparms, which are the control points, much like a lattice. The computer interpolates smoothly between adjacent isoparms, which generates the smooth surface you see in the viewport. It was a very efficient way to render a surface with the hardware of the time.
Today, surfaces can be used for hard surface modeling, ie cars, planes and environments, although their use is fading quickly.
Metaballs can be used to simulate some "special" fluids, like ferro fluids and soap bubbles. Most of the time though, they are just a cool effect for motion graphics :). Specially in abstract designs.
Nurbs Surfaces can be used to model any object with smooth surfaces. Their strength (compared to poly modelling) is handling complex curves smoothly. That's why they are the preferred modelling method for industrial design and manufacturing. There are even machines that take NURBS data and cut pieces for you.
Note that NURBS in Blender are underdeveloped in comparison to poly modelling.