What's you opinion?

I assume you're talking "powered subs"?
I think, from an audiophile point of view, that subwoofers tend to "generally" get a bad wrap as being "low-fi" often. Really, it's my experience that, as individual components, A VAST MAJORITY OF SUBS(all shapes, sizes, and price points) are actually VERY VERY GOOD PERFORMERS POTENTIALLY, and are proportionately of a higher performance potential than MOST audio gear on the market! Let me clarify...
...What I find is that THE MAIN REASON for "POWERED SUBWOOFER'S" getting the rep they tend to is due more to POOR SET UP, CALIBRATION, LOCATION, AND INTEGRATION EXECUTION THAT USUALLY TAKES PLACE WITH THEM! Subwoofers are the single most placment critical components in the system largely, and people generally don't have a clue as to how to approach a subwoofer! Overall, especially since subs are mostly "powered", they have the potential for great control over Passive speakers and such, and will handle dynamics and transients a bit better on the whole.
I think people could get much better results sonically with subs if they knew more about how to set em up in the first place!

In response to Gmueller's comments, I find that THE VAST MAJORITY of people setting up sub/sat systems have THINGS WAY WAY OFF in terms of "IDEAL"! I do however find that you can get excellent, to phenominal results with the right gear, properly set up...even if the mains/sat's only play down to roughly 80 hz! The key is proper coupling with the room at the critical "crossover point" for both sub and sat's, balanced/flat frequency response for sub and sat's(usually not so good, do to user error and inexperience), proper phase between sub and sat's(definitely at the crossover reigion), and proper level matching. if you can pull all that off(takes some experience) well, you'll have dynamite sonic potential(acoustics and set up for soundstage is the rest)!
Of course, some subs will play "tighter" or with more authority up into the higher registers of the bass than others, just as some subs are more "accurate" sounding than others. A powerful, yet not so accurate sub musically might keep your potential down. Quick, accurate, dynamic subs, that blend well from a crossover standpoint, and play higher up better than others, obviously have an advantage. Higher "Q" subs are going to generally sound "more controled" and accurate on the whole. It's always a compromise, especially at the lower price points.
Still, there's no reason that you can't get the same potential "world class" results from properly setting up a sub sat system, as you can with an integrated full range speaker system! Infact, you have more flexibility with the sub/sat system. Still, unless you know what you're doing, you can do "more things wrong", or less than ideal with a sub sat system as well...DOUBLE EDGED SWORD!
Still, I know what I'm doing, so I like that option for a lot of applications.
Hope this helps