Traditional Salkantay: Classic 4-5 day route, Salkantay pass, panoramic landscapes and arrival at Machu Picchu.
Salkantay 3D: Shorter 3-day version, highlights Laguna Humantay, Salkantay pass and arrival at Machu Picchu.
Differences: Duration, highlights and approach, but both reach Machu Picchu and offer beautiful scenery.