It's been trodded by tens of thousands, but the Muir Trail was fun for me, back when. You can start on doing the whole thing, say in three parts, as I did. It's a fine tour of the High Sierra, taking about 2 weeks in travel time, with so many peaks along the way.
I first went to Whitney via South Lake (100 miles in 7 days), then back to Devils Postpiles, and then to Y Valley. This sees all of the parks. A year later, I finished it by going from Devils Postpiles to South Lake, bagging Agassiz as a finish.
Trouble with three or four guys is transportation. I just bummed rides or hitchhiked, easy to do back then (early 1970's), Shuttles now are $$$.
If you wish lots of miles, it's a good way to go, the trail being like a freeway. Otherwise, I just went on climbing base camps, bagging peaks.
There's the Sierra High Route, and countless other ops to do in CA, about all that is doable in summer. The Lost Coast may have fog, then. And you can do similar with the PCT, walking sections of it, just that you'd probably wish a shuttle. It's all glorious, and you can do a loop hike if you wish to start back where you started. For some, the CDT may do as well. There is a Uinta High Trail, Toiyabe Crest Trail, and more.
If you like bagging peaks versus miles, I did many such trips, some on my website at Peaks Archives and elsewhere.