I'm pretty biased...but I'll try to stick to the facts
I hate Comcast because all our bill ever did was go up, up, up. The "special offers" are great to get you in the door but after that...
Before you ditch Qwest, do some checking to see when/if they might be doing the FTC (fiber to the curb) buildout in your area. They are spending a TON of money putting fiber in the ground. Also, check to see if they'll offer you a VoIP line for your home phone.
As for reliability...Not sure what your experience with Qwest DSL is but in nearly 8 years I can count the times my DSL has been down on one hand and only once where I had to actually call for service vs. just rebooting the modem to restore service. Comcast on the other hand for me was down a LOT when we had it. And it always pissed me off when I would call and they wouldn't send anyone out until more people in my area called (I think the magic number was 3 in the same area). Not sure if they still do that. My co-worker at work has Comcast for cable TV and use to have it for internet. He loves the TV, hated the internet reliability. Said it was done all the time during the day when he tried to work from home. He dumped it and went with Qwest DSL when it became available in his area.
My other complaint with Comcast is the "shared" service which regardless of what their cute commercials state can cause the network to slow down...Look to see if they offer guarantees that you'll get the speed all the time that you are paying for.
Good luck with whatever you choose.