I can only add . . .

The two share major components, like steering, suspension, brakes, transmissions, and a few engines. The 300E is longer, wider and has more interior room. However it is also heavier and a bit less sporty around turn.

The 190E has less interior space, particularly in the rear seat and not much adjustment for drivers in the 72" or more range.

As with any used Mercedes, whether it's a good purchase at this date will depend on the previous owners maintenance. Parts for both are readily available and both are probably one of the last series that home mechanics feel comfortable with.