Tom Andry said:
Size of box, extension, responsiveness, aesthetics, correction system, other (fill in the blank).[/I]
COST (other)
Accuracy (other)
Extension
Responsiveness
System Blending (other)
Aesthetics
Correction System
Size of Box
EDIT: I added cost as the most important factor. Yes, cost matters most. I have a budget and when I have that budget, it is then and only then that I can even begin to think about what I will be able to get with that money. Sure, I may want that 18" killer sub, but if my budget is $300 and that sub is $3,000 then what does ANYTHING else matter? It doesn't! But, when getting back to what I consider after determining my budget...
Hands down the most important factor for me is getting accurate sound from the sub. Not one that is boomy or artificial sounding, but has a nice tight controlled response. This plays directly into items 2 and 3 which is the low end extension and how well it responds when send the frequencies it is supposed to handle.
Now, all that bass and power must be able to blend in with the other speakers in my system perfectly. Simply giving me 100dB of great sounding bass won't do it if it jumps out from the rest of my system completely. It really must simply be there as an extension of the rest of my system.
The last 3 items are way down there for me. As I think a nice looking box is somewhat important for both selling it and showing it off to friends. Then the correction system will matter most I would think in a poorly designed room or at a poor location. If the correction system greatly ties into the accuracy of the sub, then I might just move this up to number two. But I don't have enough info on correction systems to say how much of an improvement they truly make. So, some more honest info from reviewers on correction systems would be an article I would like to read.
Finally - the sub should be as big as it needs to be. That is, for some size will matter a great deal as they need it small to be hidden or they want it huge to compensate for personal misfortunes. But, regardless of size, it should be the best possible sounding sub that can be made at that size. I will use a 3 foot tall subwoofer though if it gives me better sound for the money.