This beautiful part of Italy is not a hidden gem anymore but it is still a very charming destination for just a few days. I just returned from three nights staying in the town of Vernazza and was able to experience hiking, train ride and boat ride. You can stay in any of the towns and still enjoy all three activities.
Monterosso Al Mare offers more hotels, Corniglia is smaller and less crowded. To avoid crowds on the trails, make sure to start hiking around 8.00am. If you are driving, you need to reserve a parking spot in advance on line. You can reserve in La Spezia or Levanto. For the real serious hikers, along with the main trail going from one town to the next, you have many other trails in the park. They are quite steep but it is worth every pain you might have the next day! You will be by yourself and you will have the most amazing views.
On your next trip to Italy, do think of Cinque Terre if you are traveling in the northern part of the country.