A quick look will show the Ertl Cobra to be superior in most ways but this is not to say the Road Legends version is without merit. Neither car has been modified or detailed.
The paint color and stripes look more accurate on the Ertl version, though the RL version has a nicer looking chrome roll bar. The overall body shape on the Ertl seems to look better. The lights and other small trim items look better on the Ertl. The Ertl also has the hood scoop rivets which are missing on the RL version.
The RL version has
an opening trunk which is a nice detail. These two models have
differing body shape details, but there is no reason this cannot
be attributed to having used different 1:1 Cobras to model. I
have seen Cobras with more and less pronounced fender flares as
on the two models pictured. The wheels on the Ertl look better,
they are molded sharper and deeper though both sets are well detailed.
The tires are Ertl are much superior in detail.
The Ertl interior has better dash details and the floor on the YM is grey not black which kind of ruins the effect on it. The overall interior effect is superior on the Ertl.
Both engines are well detailed. The Ertl has the single carb version with the hood scoop bucket while the RL has the dual carb version. Both are accurate to 1:1s since many different versions of the 427 (and 428) were available in Cobras at different times. The Ertl has more and more well done additional details under the hood such as radiator tanks, oil filter and oil cooler and the Ertl also has plug wires which are missing on the RL. The Ertl uses a hood prop rod and the RL simply allows the hood to open far enough to stay open by itself.
The undercarriages are similar, but the Ertl seems to be molded cleaner and sharper. Notice the better looking tires on the Ertl. I personally like the white side pipes more than the chrome ones on the RL version.
The greatest advantage held by the RL version is that it is readily available and usually at a low price when compared to finding some of the Ertl versions. The Ertls, depending on color, can command inflated prices in the aftermarket. Both models are well done. Though I would pick the Ertl first, the RL version is probably one of the better done RL cars of all time.