The major factors that you need to take care of are the frequency [in Hertz], the power [in Watts], and the drivers. The higher the Hertz, the lesser the frequency of the bass you will hear. The heaviness of the bass depends inversely on the Hertz value.
Coming to the watts, the higher the power delivered, the greater is the audio output. This becomes important when you have to connect your speaker to an amplifier. The drivers are equally important, however, they are not quantified.
The kind of drivers present in the speaker affects the audio quality. Woofers and tweeters are the most important ones, but a third mid-level driver will give you clean, clear-cut audio across the audio spectrum.