Hamachi (Yellow Fin tuna) is my favorite fish for sushi or sashimi, and I enjoy Negihama rolls (yellow fin with green onions, wrapped in seaweed) at least a few times a week, and have been doing so for decades.
As part of my New Year's celebration, I've been having Hamachi for the past 3 days (yum!)...
With that said, I only purchase tuna from Japanese food stores that I trust, which is pre-cut into a block that I can then further slice depending upon what I am preparing. It's way cheaper than eating out at a Japanese restaurant (plus my wife is Japanese, and her sushi rice is way better than most Japanese restaurants).
ADG