Withou snow, which way is more pleasant/faster to get to the NE end of Barrett Lakes from Bishop Pass: via Thunderbolt Pass or staying longer on trail but with potentially less talus via Knapsack Pass?
I agree that Thunderbolt is more direct but.... T-bolt is much rockier, has more boulder scrambling and entails more vertical gain & drop to get to Barrett Lakes. If you're climbing light & fast with Palisades as destination I'd recommend T-bolt pass. But if you're carrying an overnight pack and planning on making base-camp at Barrett Lakes I'd reccomend Knapsack Pass. On my last trip we carried multi-day packs to Barrett Lakes. We entered via T-bolt and exited via Knapsack. The loop is a nice option for more variety of scenery.
Thunderbolt is faster but probably less pleasant overall. If you have the time to burn I'd say Knapsack is nicer. Thunderbolt is a bitch, especially coming back over to Bishop Pass. Quickest way back though.
We just had the same decision to make a few weeks ago and, hands down, opted for Knapsack Pass as we were humping heavy, multiday loads full of food and gear/pro. Knapsack isn't bad at all with a week's-worth of gear on your back, especially if you stay toward the center of the pass on the Bishops Pass side. Otherwise, navigating the large boulders can become a bit cumbersome.
I've done both with multi-day loads, and even with a big pack, I prefer Thunderbolt. If you drop down on the trail from Bishop Pass, the cross country is pretty mellow, and the final talus bashing is worth the distance saved--just me. Using one or the other on the way in or out does make a nice change, and the view from Knapsack is spectacular.