what is the best exhaust for a 2011 z-71 1500 sle?

This is really a broad question. Because of the nature of exhaust systems, its hard for one person to give advice on the best one. Its all a matter of taste. If you want just plain loud, then consider straight piping the truck. That's the cheapest route for the loudest growl. However, you are going to want to commit suicide if the exhaust drone bothers you (drone is the constant irritating exhaust note you hear inside the cabin when cruising). Borla and magnaflow are both very reputable exhaust manufacturers. They are on the expensive side, but you do get what you pay for. Exhaust drone is also minimized with sets like these because they are well designed and thoroughly tested. Another question to ask yourself is whether or not to keep the catalytic convertor, remove it (illegal in most states, but not often enforced unless in a state with emission tests), or switch to an aftermarket high flow cat. Each of these options will effect the sound of the exhaust you eventually use. Finally, deciding whether or not to upgrade your headers will also affect the sound. Performance headers will free up some nice horsepower and give a great deep growl. However, these can be expensive. Basically, shop around and decide what you can afford and make a list. Once your done, go to youtube and search for your truck with those exhaust systems. Youtube is flooded with soundclips like that. Use earbuds when you listen to them. Try this one: http://www.youtube.com/watch?v=Xbn5GIm8qHc