The choice between using PLA or ABS is going to depend largely on your printer’s capabilities/features as well as what you want to print, and the qualities you want the final print to possess.
ABS melts at higher temperatures, which means your machine has to run hotter in order to use ABS filament. It also is less sticky than PLA, and use of a heated print bed is recommended to help the material adhere to the bed while the print is in progress. If you are considering working with ABS – check your printer’s specifications to ensure that it has a heated bed, and is capable of running with the temperature tolerances of ABS filament.
By contrast, PLA cools quicker and has better adhesion to the print surface, not requiring a heated bed or the hotter process temperatures of ABS. This means that generally you can print faster with PLA. However, PLA’s lower melting point makes it more prone to warping/distortion if exposed to extreme heat post processing than ABS.
In terms of finishing your prints, ABS is soluble in acetone, which means you can wipe it over to smooth out any bumps or blemishes. Acetone has no effect on PLA, but PLA generally produces smoother prints from the start. PLA also tends to have a glossier finish and is more rigid than ABS. In general, those printing for display purposes will most likely prefer PLA while more professional applications will generally call for ABS. Finally, some printers will only work with one filament or the other; be sure to check your printer specifications before purchasing filament.