I have had sirius.  Its pretty cool, especially if you travel a lot.  Mine would go out under bridges/overpasses, but maybe thats because I didnt mount the antenna on the outside of the car.   
I have heard for XM in some cities you dont even need an antenna because there is boosters around the city.  I dont know if columbus is like that or not though.   
If I had to do it over again, I would probably get XM instead of Sirius.  Keep an eye out, a lot of times crutchfield and other places run specials like buy a setup get a year free or whatever.   
I dont think you will regret it.  The music is worlds better than local stations too.  Lots of underground stuff and hardly any mainstream BS.   
*also, make sure you get an XM ready reciever.  Do not go through a FM modulator, because you lose a lot of sound quality.