As an emergency manager, I recently sampled each of these bars so I could plan for disaster supplies for a new school we're opening this fall. For taste, I like Mainstay. It has a lemon flavor and its sweetness is what you'd expect in a "cookie-bar" type of food. By comparison, most others are a bit more bland. Someone at our agency bought ER Bars about five years ago and I cracked one open in a management meeting for us to sample. Whatever separate sections were in the bar for portion control were now fused together. The entire bar was one brick-like stone tablet. As for taste, it had a distinct vitamin-pill scent and flavor; bland, but edible if that's all you have. For our school (Kindergarten and first graders), I chose the Datrex which stands out in one important category: individually wrapped portions. One meal consists of two individually wrapped "wafers" that taste kind of like a coconut macaroon. Not as sweet as you might expect, and light texture (unlike the overly dense ER Bar), Datrex only has six ingredients: flour, shortening, sugar, water, coconut, and salt. Nothing else. When dealing with youngsters, I cannot imagine trying to cut or break those ER Bars into manageable pieces for them.
I also know that the S.O.S. Food Labs brand ration comes with individually wrapped pieces, but I haven't sampled them. For adults, I'd still go with Mainstay. While not individually wrapped, the bar is made up of individual sections which remain separate even past the expiration date.
What do these foods have over MREs? It's simple: low cost (how about $4 for a three-day ration?), ease of storage (five years in sub-zero or 130 degree temps), and no preparation (just open it and "enjoy").
For large corporations and agencies, personally, I'd recommend a combination of both types of food. Cookie-bars for shelter victims and others not involved in strenuous work. MREs or Mountain House for rescue teams, damage assessment teams and the like.