Volvo recommends NOT using a Synthetic for the first 10,000 miles. I think this is in the manual, but I heard it from the dealer that sold me the car, and also from a different dealer where I get my oil changed.
As for which brand synthetic: I use Mobil 1 because Mobil seems to be committed to synthetics (they have had a complete line for a long time, including a lot of commercial products), as opposed to the various "me too" offerings from some of the other companies. Also, I prefer Mobil 1 over brands such as Red Line and Amsoil for convenience (Mobil 1 is readily available at many retail outlets). However, I have no credible evidence that any brand is better than any other brand. If I had such info, I would certainly go out of my way to use that brand.