Its not just opinions its the fact that many quality speakers like Wilson, Focal, Klipsch, Paradigm, Monitor Audio, PSB, Kef, RBH all have been tested and measured
. They have graphs available that can get you picture of how it will sound. Freq response (flat, peaky, ect.) off axis response, ect.
Heres a good example http://www.ascendacoustics.com/pages/products/speakers/SRT/srtmeas.html
Good manufacturers provide that kind of data to give people an idea on how the speaker might sound and whether it was competantly designed. Thats how guys on here can make some kind of determination on whether its a good speaker, a bad speaker or a great speaker.
Also price doesn't equal better. Theres many speakers out there some much cheaper that measure better or more ideally than Wilson does. While Wilson is nice speakers just because they are uber expensive and fancy doesn't equal better.
Your looking at $50 speakers, the manufacturer isn't going to put much effort into sound quality and craftsman ship they way higher end speakers will.
You'll also see terms like bright, warm, bloated, ect... Bright is that the listener thinks the highs are louder than the rest of the speaker, making it seem uncomfortable to listen to for any lenght of time. Warm means that the listener has to turn the volume up to get the desired high freq response (like the highs are somewhat muted compared to the woofers output) Bloated usually means bass is way too much and doesn't sound right.
What people was trying to get across earlier is that some users will perfer the bright speaker or the warm speaker or vice versa.
IMO those 3 your listed wil probably all sound about the same and I would base my discision on long term reviews about how the speaker has held up to normal use and if it still works after a year or what ever time lenght.