With a ported subwoofer, you get sound from the woofer and from the port. If it is well-designed, what this means is that it will extend the depth of the bass before the frequency response starts to drop-off, because the port will be tuned to provide bass at the point of drop-off of the woofer. However, one does not get something for nothing, so when a ported subwoofer does drop off, it drops off faster than if it were sealed. But before the dropoff point, you have more bass, which can be deeper than a comparable sealed subwoofer. You can look at the frequency response curves that SVS provides for the PB-1000 and SB-1000 to see this for yourself. You can see this principle in one graph if you look at one of the ported Ultras (either cylinder or box version) and see the different response curves with various numbers of ports, and with all of the ports blocked (or in other words, sealed).
So, for people with an unlimited budget and unlimited room for subwoofers, a bunch of sealed subwoofers that are EQed to boost the deep bass is probably the way to go. For people with more normal situations, I think that typically a ported subwoofer or two is the way to go. Just keep in mind, when the drop-off occurs, you are not going to be able to EQ it or do anything about it; the depth of bass that it has is all you can expect to ever be usable, even with more than one.
For most people, I think the PB-1000 would be the better choice. The SB-1000 has one other advantage, though, and that is that it is smaller. Some people do not want a large subwoofer, and that limits their options.
