On the cable side, Comcast "competes" with Broadstripe. Broadstripe has both terrible customer service and poor internet service. Broadstripe also happens to have a bunch of apartment and condo complexes covered in an exclusivity agreement. Broadstripe makes Comcast look great in almost every regard.
On the DSL side it's true that Speakeasy is available, but if you are willing to ignore customer service, Qwest DSL is almost always dramatically cheaper. It's a good option, but sometimes not available above 1.5mbps, even in extremely central areas like Belltown, which is a neighborhood of condos and apartments directly adjoining downtown.
I'm on Comcast residential now and I'm pretty happy with it compared to my past experiences with all the companies I mentioned above, but next time I move within Seattle I now know one of the top questions to ask is what kind of internet access options the place has.