The grass fed vs grain fed debate is huge, even among cattlemen. My brother has a herd of beef cattle, and they are primarily grass but supplemented with hay and some grain in the winter months. For all intents and purposes, classifying the sirloin as a "healthy option" has little to do with what the animal was fed. It's really because of the cut itself. The loin area is one if the leaner parts.
Personally, I prefer tenderloin (usually even leaner than sirloin), but I'm also very spoiled by our homegrown variety. I probably wouldn't eat steak on a ship in favor of a variety if seafood...which I can't get locally.