Hmmm, I can't really tell what you mean by "the rim." Would that be the ridge between the right-off-the-trail lake and 11393? Or would that be further downstream - just west of all 4 of the upper lakes?
I'm curious about the very lowest lakes (down at 10,750), because they provide possibly the best take-off point for Knapsack Pass. However, I too thought it looked like the photography and the view of the crest would not be as good from there. The further south you wander along those lower lakes (and the further from the trail), the more Isosceles and Columbine Peaks would obscure your line of sight to the crest.
I wonder about the second lake down - 11388 - its north side. I wonder if that could be a good compromise in terms of wind exposure, line of sight to the crest, not camping on top of a bunch of other groups, and access to Knapsack.
We will have a group of people with mixed abilities. We have a layover day. I want to take the more ambitious half of the group over Knapsack to the lower Barrett Lake and back. Ideally we'd return to Dusy Basin via Thunderbolt Pass. In that case our loop-hike would be about the same distance regardless of where our camp is based. However, if there is even one person who becomes scared of Thunderbolt and prefers a return over Knapsack, it would make a lot more sense for our Dusy base camp to be located closer to Knapsack rather than at the highest lake.
The other part of the group - more scared of heights, not in as good shape, want to take it easy, etc. - can do a dayhike, either exploring around Dusy Basin, or maybe down the trail switchbacks to get a good view overlooking Leconte Canyon. I can't recall how far down it is to that giant juniper, or to the waterfalls. The waterfalls may not be much of a spectacle anyway, given that we're talking Labor Day weekend in a low-snow year.
We are not interested in fishing - really just alpine scenery. And we'll have one, maybe two professional photographers among us, so maybe I'll be persuaded to camp exactly where sssdave tells me