What would be a good set of Rails

For a mid-length (16") AR with a RRA Upper?

thats an EXTEMELY broad question, partner... what do you have on it now? do you have a fixed FSB? what is the weapon for- duty? plinking? home-defense? do you run a light? VFG? what distances do you shoot?

have you read all the AR stickies?

What are your priorities?
What do you want the rail to do?
Weight?
Fixed front sight, or low-pro GB?
Budget/value?
FF or not, does it even matter to you?
What do you want to mount to the rails?
What length do you want, and if not sure, do you want the ability to hold out further on the rail than on the standard HG, or does it not matter?
Does it need to be entirely made of rails or would it be acceptable to mount rails where you want them?

Basically, what do you want it to do and how much are you willing to spend?