PrusaSlicer is a fork of Slic3r Bambu's slicer is a fork of PrusaSlicer Orca Slicer is a fork of Bambu's slicer and also pulls in ideas from super slicer (another PrusaSlicer fork).
In other words, they all share a common lineage. Each adds quality of life improvements over the fork, at least in theory. It's possible those quality of life improvements will make it back upstream to the thing that was forked.
As for specific examples, Orca Slicer has a somewhat different set of tuning parameters, some unique-to-it quality things like scarf seams, built in tuning prints (temp towers, EM multiplier, pressure advance, a test to find your max flow rate, etc) a revamped UI, etc. I haven't compared the two in a while, so it's possible that some of this has made its way upstream by now.
Get a hear rate monitor and do High Intensity Interval Training (HIIT). It's by far the fastest way to increase your stamina if you're untrained and even if you are trained it's a very effective means of increasing your stamina.
This is backed by science.