I did the LT last summer and will be doing the JMT in a few weeks - I’ll give you a comparison feedback then. I’ve done sections of the JMT in the past and the biggest difference (besides altitude) is the view. The Sierras provide frequent expansive views. The LT is a green tunnel, most of your view is restricted by the canopy. Beautiful, but a different kind of beauty.
As far as direction is concerned, most hikers hike northbound. The southern part of the trail is more gentle, the mountains in the north are much steeper, rockier, harder. The idea is to warm up in the southern part of the state so you are ready for the northern part of the state. There are also more views from the northern mountains, so as you head north the scenery gets more dramatic. I’ve heard some hikers say that heading southbound, they got used to the views up north and found the constant green in the south boring. That said, they’d warmed up in the north and could fly through the rolling southern mountains (begins to sound like a mini-AT).
I did the trail in July which meant that I was sharing the first 100 miles of the trail with AT hikers. This section of the trail was crowded. I liked the people I met and picked their brains for beta on loosing pack weight, but the quiet after the trails split was also nice. Heading northbound you are more likely to run into other hikers and form your own little community, southbound would be a more solitary experience.
Both hikes are beautiful, I’ve met people who’ve done the trail multiple times and everyone has their favorite- usually the direction they hiked first.
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