Used to run in Pegasus in college and of course ran workouts in the streaks that they gave us. In high school I ran in Nike free 3.0 and 5.0 for about a year or so and then was told I shouldn't once I got to my college team since the coach thought I would get injured shortly after arriving.
However I have always felt better in flats, maybe because I built up my lower leg muscles in the frees, and because I have wide flat which seem to get too jammed up and compressed in trainers. So after college started training pretty much exclusively in the Adidas adios but they are quite narrow even sized half a size up I would make it work just by barely tieing them up.
My favorite flats which I feel are totally being slept on my modern runners are NIKE WAFFLE RACERS. In fact they have a few cool colorways on Mike's website and yes $85 plus shipping may be a bit steep but they feel so good and natural. I find them to be even better than the streaks for daily running and the classic mesh/nylon allows for ease of motion, actually was thinking of making a thread on them today since I love them so much. Made in '77 and the re-release from 2019 are so awesome! Maybe you have to work in them slowly but you'll be glad you did it's like not even thinking about your gait/footstrike, they just seem to dissappear on your foot. Retro looks are a plus after you wear them out (long long time) make great casual shoes, haven't worn through my first pair yet and I found they feel better the second or third week as they break in.
Nike Waffle Racers FTW
There's some green/yellow on another link