Gilbert track is made from a relatively heavy gauge steel and the railhead is almost flat making for a large rail to wheel contact area. As Adriatic pointed out, traction is good but the susceptibility to sparking is greater. In a layout using Gilbert track virtually all the resistance and voltage drop is in the track connections and the brass sliding contacts in the turnouts. The turnout contacts can be cleaned to eliminate the resistance. Track pins which are solid steel must be clean and tight. I also use a light coating of conductive grease on the track pins.
Since Gilbert track is not plated it can be sanded or polished if desired. There is a process called burnishing that some S gauge operators have done to their track to improve performance, it is a lot of work. There are posts here about that process, search on burnishing.
GarGraves S track is made from a lighter gauge of steel and stainless steel is available for optional order. The railhead is not as flat as the Gilbert track resulting in a smaller wheel to rail contact area. This contributes to less sparking. Compared to Gilbert track the GarGraves also has a smoother finish which contributes to less sparking as well. The GarGraves track pins are brass and seem to work ok when joining two pieces of GarGraves track.
If you really want zero sparking use solid NS rail. My permanent S gauge layout uses MTH/SHS .138 NS rail. There is never any sparking.
