I have the c330, which is the older version of the 550, and a friend of mine has the nuvi. I really love my 330, and the 550 comes from the same family, so I would expect great things from it. If you are wanting the traffic info, then even more power to the 550.
I believe you do have to pay a service fee to XM or someone to get the live info, but that's expected. I am not positive, but I think they both play mp3s. Mp3s on the nuvi sound horrible, because they play directly out of the unit.
Not sure how the 550 sounds, but I assume its similar. More.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.