Instead of framing this debate as an either/or proposition, let's see where the two formats overlap.
1. Both digital and printed books are soldiers in the battle to promote the written word. Mass audiences today overwhelmingly consume oral entertainment (TV/movies), which actually discourages critical thinking.
2. Time alone without distractions is still required.
3. Semantic processing - how a reader understands and remembers a story - occurs in the same fashion regardless of format.
4. Contemplation, reflection and self-examination are the desired result of each.
5. Elements are the enemy of both. Drop your e-reader in the bath and most likely it's kaput. Same with paperbacks or hardcovers.
As British novelist Nicholas Shakespeare has said, a writer shouldn't think of him/herself writing on paper or writing on a screen but on a human heart.