I checked out the base chicken sandwich at Sonic the other day. On the menu this is just called the Classic Chicken Sandwich, grilled variety. It was pretty much your basic fast food chicken sandwich from a restaurant that specializes in burgers:
The chicken sandwich is no frills. It is delivered on a nice Cibatta bun but is otherwise plainly adorned with mayo, lettuce and tomato. The chicken breast itself is unappetizing when examined naked. The entire sandwich is dry and blah. Very much like the McDonald's chicken sandwich reviewed here and here.
But for whatever reason, Sonic's chicken entry does not come with cheese or bacon. This makes the entire sandwich seem even more plain and the chicken just that much more lonely.
I recommend Sonic for the burgers, or the hot dogs. And of course for the tots. But skip the chicken until they come up with something better.