Bach 5MV vs Marcinkiewicz 14
The Marcinkiewicz 14 has a wider cup diameter, the Bach 5MV has a larger throat opening.
Cup Diameter
The Marcinkiewicz 14 has a cup diameter of 16.31 mm / 0.6421 in compared to 16.25 mm / 0.6398 in on the Bach 5MV — a difference of 0.06 mm / 0.0024 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Bach 5MV has a wider throat (3.81 mm / 0.1500 in vs 3.73 mm / 0.1469 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.