How to choose a right 3D printer filament type?
Determine what properties you need the filament to have.
There are a very wide variety of filaments because they all have somewhat different properties.  You need to determine what properties you need your final print to possess.  For instance, ABS can be smoothed used acetone and PLA is biodegradable. More exotic filaments could be conductive or be extremely flexible. Do not neglect to consider safety of the plastic in your application. A full list of properties is too broad for an appropriate answer from this site.

Determine what you printer is designed to handle.
Most printers can handle PLA and ABS with little issue but higher temperatures are required to use some materials such as nylon and polycarbonate.  Determine beforehand what your printer is designed to handle.  This includes determining whether you have and appropriate heated bed or other accessories.

Determine what you can afford.
Printing not only requires the cost of the weight of filament in the final print but all of the support structures and misprints you produce. Not only should you look for inexpensive filaments, but you should look for ones that are good enough quality you don't waste time and money fighting problems with the raw material.


All in all, this will vary case by case.  I would recommend that you start with PLA or ABS as they are common and relatively easy to work with but that you do your own research into what each individual filament type has to offer..