If you opt for the Sirius option, be sure you don't get ripped off. Here's my story:
I just bought a brand new Mazda 3. I wanted the dealer to throw in the Sirius radio, which they price at $400. He refused so we agreed to go halfsies. Now this is already too much if you ask me because I can get a Sirius tuner at Best Buy for $129. They ordered it and when it came in I asked to get have it installed and they asked for $225. I told them they were crazy and if I ordered air conditioning they wouldn't charge me to install it. Especially when Circuit City only charges $64 for installation. Now the only reason I wanted to go with factory part and dealer install is because I wanted to see the chanel on my factory head unit and be able to change the channel on my steerting wheel, not like the after market units that have wires all over the place and a palm pilot looking thing hanging off my dash somewhere. After arguing with my salesman for 15 minutes I got no where. So I called Mazda and they are going to send me a $100 gift certificate to the dealer. I decided to install the radio myself and use the money for oil changes or whatever. So moral of the story is be careful when getting the factory unit and make sure they include installation when they charge you an arm and a leg for the damn thing.
Bry