My first choice for a little hole in the wall joint is Coyote Bluff on S Grand St.
my second choice is Hoffbrau on I-40.
There are numerous name brand steakhouses in Amarillo that are typically good.
If you want a popular tourist stop hit the Big Texan on I-40 and try the 72 oz steak. You will even be filmed. They actually serve good meals.
Finally if you want the best steak around you can come over to my place.