Hi Tin, which speakers are you considering adding the sub(s) to? What other speakers are you thinking about? I think this is as important as the subject of whether subs are better or worse.
I really disagree with the broad strokes of the brush that state that subs are definitively better or worse, or that they only apply to the lowest frequencies on your music of choice.
I recently added a pair of Kinergetics SW800/SW800C to my ML CLS's and I can tell you it is a whole different world. We're talking exponential imrpovement. And, not just more "bottom end". In addition to solving the CLS's LF rolloff problem, there's more detail, better imaging and a bigger soundstage. Now, my sub system (including crossover) were specifically designed for my speakers and allow me to use a 100htz crossover point with no negative effects, taking much stress off the panels. Additionally, the SW800's are a line source (just like the CLS's) down to 200 cycles. In short, it works flawlessly.
Now, the REL's and Vandersteens didn't work at all with my speakers, and these are considered to be some of the best subs out there. I couldn't find crossover points or slopes that didn't kill the inherent speed and transparent qualities of the CLS's. And, though some claim that the Vandy's and REL's are "fast", they were obviously lagging behind the main speakers -- big time. Yet, these subs can work great with other speakers.
I guess what I'm trying to say is: "it depends". So, I'm back to "what are you using now and what would you contemplate using as an upgraded speaker sans sub?"
