For me, in the summer on the main Whitney Trail, or on any other trail, running shoes work perfect - I've done it in sandals too, but I like the running shoes best - trail runners have a bit more traction so they are good. I only wear boots in snow when I'll need to kick steps or wear crampons, and then it's mountaineering boots. I switch from the running shoes to approach shoes when I'll be traveling off of a trail because I like the sticky soles for scrambling.
Footwear is a personal choice - what works for one person does not always work for another. So, you'll have to figure out what's best for you.
