Ones that go on the top of the cab and look OEM... Or just good horns?
I put a set of these beneath my cab pointed straight down.
They sound good and are plenty loud. I did however buy a different solenoid valve to allow for a larger air flow, the original one only has like a 3/16 hole for air to enter. The one I replaced it with accepts a 1/2 DOT air line. The electric valve can also be removed if your setup already has a manual valve plumbed inline somewhere.