Curry 2 BBC vs Kelly 3C
The Kelly 3C has a wider cup diameter.
Cup Diameter
The Kelly 3C has a cup diameter of 17.02 mm / 0.6701 in compared to 16.97 mm / 0.6680 in on the Curry 2 BBC — a difference of 0.05 mm / 0.0021 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a very deep cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
Throat diameters are essentially identical at 4.06 mm / 0.1600 in, so resistance feel will be comparable.
Material
The Curry 2 BBC is described as unspecified, and the Kelly 3C as Lexan polycarbonate. Material affects mass, warmth, and how quickly the piece responds.
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.