If you can get hold of detailed specs for the speakers like the frequency response/sweep across the audio spectrum, how impedance and phase varies, till what frequency the low frequency response is flat, etc., then you will be able to make a more informed choice.
The ideal response for amplitude (y) plotted against frequency (x) must be flat, or nearly flat from 20 Hz to 20000 Hz. But real world speakers will invariably have a number of dips and peaks. Or the lowest octave may not be left with much power. These dips and peaks will not colour the reproduction of sound too perceptibly, but they will deviate from perfect neutralness.
Similarly, if a speaker is rated for 8 Ohms nominal impedance, the impedance must stay mostly at 8 Ohms or higher across the audio frequencies. If the impedance dips to half (4 Ohms), please note that the amplifier needs to supply twice the power. The amplifier's circuitry and power supply may not be equipped to deal with such a drastic demand. Similarly, if the impedance were to drop to 2 Ohms at some frequencies, the amplfier needs to supply 4 times the power. Over-wrought amplifiers may be equipped to deal with such demands, but most amplifiers will not be able to handle such a demand. This is the reason why some speakers are said to present a difficult load to amplifiers. 8 Ohms or better across the frquency band is a benign load for the amplifier.
Also, how OEMs choose to specify the frequency response matters. Some will clearly state that (for example) the full power is available till 32 Hz. After that, it drops precipitously, say at 6 dB per octave (or may even be 12 dB per octave). So by the time it reaches 16 Hz (one octave), the perceived loudness will have dropped by half (with 6 dB per octave roll off). That's the number, but it will not tell you how it will reproduce the texture of bass. For that a listening is needed.
Also, someone here dismissed sensitivity as being not too relevant. It is very relevant. A high sensitivity speaker needs less power to play loud. For example, let's say you have speakers that are 91 dB efficient. Using these speakers, let's say your usual listening level at your listening chair/couch is 85 dB (SPL). If you have speaker that is instead 3 dB less efficient, viz 88 dB efficient, you need an amplifier of twice the power to produce the same 85 dB loudness. Alternately, you need to crank up the volume of your 40W amp to twice the power. If you look at the cost of entry/mid level amplifiers in the 40-50 Watt range and 80-100 Watt range, there is a lot of difference in cost.
My point being: don't ignore specs. They tell a lot. But not everything. You can make a shortlist of speakers based on specs, but you must go out and listen and choose what you like. Take along your favourite tracks.
