Certainly the beauty & grandeur of the Whites and Maine were very rewarding - I felt that way as a section hiker especially after finishing 28 years of section hiking by
ascending Katahdin. Re the North Woods, hiking the
Long Trail in '07 was also rewarding, especially the views of Lake Champlain - no where on the AT does one have such an extended several-days' view of a large natural body of water. My first backpack was a section of the Long Trail in 1977 and I still marvel how the view from the Glastonbury Mountain Firetower yielded nothing man-made - all I saw was mountains, forest, and lakes.
Are these places & experiences the "most" rewarding? Not necessarily - I've got wonderful memories of good AT hiking in the South - seeing wildflowers in the Spring, colorful foliage in the Fall, hiking aboving the clouds into the sunshine in the Smokies & Nantahalas, seeing bears in Shendandoah NP - all highly rewarding experiences.
And then there's other outdoor places I've been to across the country and world. Won't list them all here except for one note: I spent 2 1/2 months this summer in the Pacific Northwest, British Columbia, Yukon, and Alaska. Most of this time was in Alaska. Now there's some rewards!
I empathize with and share your positive feelings of the north country's magnificence and I suspect that in your next 30 years as you travel more, you'll also appreciate the beauty in other ecosystems as well.
And one more point about the north country: don't take its existence for granted especially in Maine with all the private landholdings. Join the MATC and contribute to the
Maine Appalachian Trail Land Trust.