Get sirius because I own sirius stock
Siriusly, (haha) you should look at the full list of available programming for both and see which one has more stations you like, and which one has more commercial free stations you think you'll listen to. They're both good, both services have enough cash to ensure the companies won't fold in the next 2 years, and both think they'll be profitable before they go broke, so neither is really a worse gamble than the other. They're both releasing new hardware every few months so although the sirius-enabled ipod was just a delicious rumor, expect similiar gadgets to be produced for both.
