A cruise can introduce you to Alaska so that you can see if you want to go back for a more extended stay. It would be hard to cover as much ground by land in a week as you can by a cruise ship. The two options are totally different.
dicoletti,
The best way to see Alaska would be to combine a cruise with at least a 4-5 day land package pre or post cruise. Personally, I would recommend you do the land portion first and then take a southbound cruise.
Nancy