Best section hikes of the AT in New England?

I have no idea what your experience is for NE trails, but I would come up for a weekend and get your feet wet on a few day hikes to see if 20 miles a day is realistic for you. I’m in Maine and am working on sectioning the state a piece at a time as life allows. Some of it is fairly gnarly. I know folks that have done the 100 MW in 5-6 days. I have only done parts of it. It can be broken up, just requires major car shuttling.

You could knock out the whole NH section in that time frame. That’s probably your best bang for buck as far as being above treeline. PM if you want any specific info.

If you have time to do 200 miles I think it would be hard to beat Crawford Notch NH to Caratunk ME(about 193).  You would get the Presidential Range and some really great hiking in Maine.  I couldn’t do 20 miles days on that stretch though and I am fairly fit.  Maine doesn’t have quite as much above tree line terrain as NH but it is beautiful, rugged, and less populated.

The hundred mile wilderness is great, though not as wild as the name might let you think as there are a few dirt road crossings.  The terrain is more forgiving and big miles more doable.  Lots of great swimming and making sure to climb Katahdin on a nice day gets you on what is likely the most dramatic alpine terrain in the east.

You also have the Adirondack High Peaks upstate which while not on the AT are among the best topography in the the Northeast.  Unfortunately it can be at least as crowded as the White Mountains and if you want to sample the best in the way of terrain it would require creative route planning that is definitely not thru-hike style.