Which island would you recommend for a 3-night stay after Phuket — Koh Phangan or Koh Lanta?

Which island would you recommend for a 3-night stay after Phuket — Koh Phangan or Koh Lanta? My wife and I (both in our 30s) will be traveling from Phuket and are looking for beautiful beaches and relaxed vibes after spending 4 nights there. We’re happy to rent a scooter to explore the island, so ease of getting around is not a concern. Which island would be a better fit? Travel Dates: 7 - 10th April