Afaik the M-Spec come with the leather steering wheel similar to the GTR one. The black car appears to have the standard (like everyone else has been saying, non M-Spec) wheel, similar to the boring Silvia steering wheels.
Check out the gearshifts. The black car looks like it is plastic and the silver car has the M-Spec leather shifter.
As far as which one is 'better', if you can check out both in the flesh, do so. Cost out how much each car will cost to repair/replace/upgrade parts to what you want and take the cheaper of the two
Definitely agree with Pred, the silver car looks pretty tired and all the go-fast bits have been removed or are shagged. I wonder what the GTR bar for GTSt is worth? May be a consideration?