We were there in May 2014.
We used the blue trail from Monterosso to Vernazza.
This trail is about 3km long and it will take you about 2 hours to reach Vernazza. The view is magnificent all the way but be aware that you will have to climb some steep steps and the walk requires some efforts, but it is definitely worth it.
In fact, you have to climb all the way up the hill that separates Monterosso from Vernazza, but when you reach the point where you can see Vernazza, you will have the best view of the day!