With food inflation playing a role in squeezing margins, Chipotle and its peers are fighting harder than ever to emphasize their respective strengths. Yum! Brands ( YUM 0.96% ) got an endorsement from David Einhorn, who argues that its Taco Bell unit is taking business away from Chipotle. At the same time, new player Chuy's ( CHUY 0.66% ) is seeking to expand across the country, and although its focus is more on the casual-dining segment than on speedy food, its price points are fairly close to Chipotle's.