The most important element is training your vision, learning the functions of the basic camera settings and how they affect an image, and other basics such as how to hold the camera steady when making an image. With rare exception, digital zoom is fairly useless. Very quickly into the "zoom" range, the image begins to degrade.
Depending on the particular sensors being compared, the differences between 16 and 20 megapixels will be minimal and trivial. Other features such as the quality of the lens, the controls the camera provides, how the camera handles for you, etc., are at least, and likely more important than the features you asked about.
Also increasing megapixels means more information is recorded providing sharper pictures. Digital zoom is really nothing more than increasing the size of the image shown and cropping to fit. You can get the same effect at the printing stage, but either way it will result in a loss of quality.
But if I had to choose, then megapixels. Digital zoom is absolutely useless. You can crop and enlarge photos on your computer and achieve the same result.
However, the megapixel number can be nearly as useless. Some cheap cameras use lower megapixel sensors and use digital black magic to increase the number of megapixels by interpolating extra information.
I'm guessing a camera that advertises 20.1mp and 10x digital zoom or 16mp with 20x digital zoom is pretty much a piece of crap and the company depends on marketing ploys like these to unwitting people to buy them.
