The 1913 Picatinny rail is the defacto mounting system since devices can be quickly and solidly attached or removed using cam levers or thumbscrews. Items are indexed using set spacing on the rail, and most items will retain a zero after remounting. Early handguards were short and rail-less, meaning you needed expensive custom mounts for front-mounted accessories. Later came a short bolt on rails that gave a common mounting system and more real estate, but the rails were clamped around the barrel and that affected accuracy.
Recent rail systems are longer and free floating, meaning they attach to the barrel nut instead of the barrel. This single point of contact means no matter how many gizmos you mount on your heater, the weight won't cause any barrel deflection or point-of-impact shift when shooting with a supported handguard. New alloys mean the guards can extend the usable area of a handguard considerably without effecting weight, stability or heat transfer performance.
What they said: "A free-floating handguard improves accuracy by isolating the barrel from external pressure. It provides a solid mounting platform for other accessories, keeps the front end light and feels more like a rifle than a giant Lego brick."
Operator Favorite: JP/VTAC Modular Handguard ($175)
Ditch the cheesegrater and use all that space on your extended handguard to actually hold your carbine instead of a foregrip. The tubular handguard with user-mounted rail sections mean you mount small sections of rail where you want your devices and leave the rest light and clean.
Also mentioned:
Daniel Defense RIS II ($400)- One of the few free-float rail systems that offers a removable bottom rail that allows the mounting of an M203.
LaRue Tactical ($250-$300)- LaRue is a traditional-style handguard with a pin-indexed barrel nut and rails that hug the barrel for a lower profile.
