Mount Lafayette and Franconia Ridge Trail Loop
This is a very popular full day hike for good reasons. On a clear day, you are unlikely to find better views in New England. Combine this with strenuous and nerve-wrecking hiking on the 'knife-edge' between Mount Little Haystack, Lincoln, and Lafayette and you have the recipe for a great day out.
As a bonus you will ascend three peaks, including the highest mountain outside the Presidential Range - Mount Lafayette.