That's a pretty good question, actually.
I'd probably go with the Spurs. If you think about it, this Team USA could conceivably lose to the Argentina NT ... and the Spurs are better than the Argentina NT.
The great thing about basketball is chemistry and experience can usually beat a collection of talent. However, if as talented as this USA roster is, it might trump that line of thought.
If the two teams played a seven game series, I'd think the series was go six or seven with either team having a decent shot.