[Buellwinkle]

There is one technical issue with Sirius and that's reception. XM uses geostationary satelites that are a fix distance from earth and orbit at the same speed that earth spins so it's very stable and consistant reception. Sirius satelites are geosynchronous satelites that stay in one orbit while the earth spins around so they are only in view for so many hours a day, that's why they need 3 satelites vs. XM's 2. During this orbit, their distance from earth hits an apogee (high point) of 29,000 miles from earth and a perigree (low point) of 14,000 miles. In theory, the Sirius system has a higher angle that it can transmit too and overcome obsticles better than XM but because it's distance and location vary greatly by day, sometimes reception is great, sometimes it sucks. As an example, with XM, I can drive under most freeway underpasses without a problem and it's consistant, if I get a drop out in one spot, I always get the same dropout all the time. With Sirius I got dropouts most of the time, even a single overhead power line can make the signal drop for a short moment sometimes, othertimes it's great. I found it irritating and was one of the key reasons I returned it.

If you are not sure which to get, get both, return the one you don't like. That's why I like to buy this kinda stuff at CC, they'll take it back up to 30 days later.