Before deiciding between those two, wait to see if Bonds, Pedro, Soriano, Randy Johnson, or Vlad somehow slips to you. If so, take him.
If you have to decide between Giambi or Pujols, take Pujols if he is elgible at 3B and Giambi if not. You might want to consider Helton. If he's in good condition he'll be better than either of those guys.
The odds of the AL MVP coming from the American League are looking pretty good.