Getting the right ISP

I have Qwest "high" speed internet, and it's terrible. It goes out every few hours. I've spend so much time replacing computers, cables, AirPorts, even the modem box, but it still is terrible. I need to switch. I have some crieteria for my ISP:

• I need something compatiible with AirPort. Otherwise, It's out of the picture.
• It needs to be fast.
• It has to be "always on." No disconnecting, no signing off.
• It has to be cheap.
• I don't care if it comes with e-mail or not. My .mac account is fine for now.

I'm thinking of getting either Comcast or Earthlink. Everyone I know has Comcast, although I like how simple Earthlink is and that I know for sure that it'll work with my AirPort.

Also, I was wondering how I can possibly extend my AirPort coverage. I may move into my sister's room now that she's gone, but she couldn't get coverage there with her PowerBook. (Her room is on the other end of the house, the furthest possible place from the AirPort, but It's much less away than 150 feet.) I also have two iMac G3s coming, and I thought I could set them up as Teleprompters in my studio, in the basement, where I don't get any coverage there.

Thank you!