Denny is correct on the proper plate placement for competitions. There are no USAWA rules that specifically address this however, but other lifting associations (like olympic lifting and powerlifting) do.
Now my personal preference for training is always flanges in for all the big plates. I’ve seen plates slip out of hands loading and causing injury. I feel its easier (and safer) to hold onto plates as you push them on and pull them off if your fingers can grip over the flanges of the plates.