I think shadow is better, even if sonic is fast shadow can slow him down with chaos control and also shadow has the ability to kill someone in a single blow. Oh yeah and shadow is serious in fights and Sonic isn't so it can get him killed easily. Easily distracted (Sonic) and Shadow can hold his own against dark sonic which is a transformation.
Shadow is by far the best out of all these characters. In recent times, Silver hasn't even been born yet, doesn't come close to Shadow's speed and has a VERY annoying voice. Sonic is very cocky (though Shadow is too), has a voice that people can live with, has no chest fur, has no guns, and doesn't have any mysterious or horrible past that makes him the bad boy that all the girls are drawn to. If I missed something then add plz! And just like the song says, "All hail Shadow, Heroes rise again."