I'd take Tim for several reasons. Mostly because of his longevity, commitment to team ball, the fact that he doesn't let his ego trouble the chemistry of his team, superior defense in every way possible, and commitment to stay in shape every single year. Oh, and possibly the biggest reason why I'd take him over Shaq is because he's willing to sacrifice millions of dollars so that he can have a better team around him.
I'd take Duncan. He'd stay at the top of his game longer and win more championships. Shaq after 2003 has seen a steady decline in production. Duncan has had a much more consistent career.
Uh, Shaq was in his 11th season in 2002-2003. Duncan is in his 11th season now.