Comb Material

Comb material does not affect the the sound of your harmonica (assuming the comb is flat, making an even mating surface for the reed plate to the comb), but it does affect the feel. Choices are commonly plastic/resin, wood and metal. The issue of wood combs swelling is less of an issue these days. The most notorious in the past being the Hohner Marine Band, but they're now triple-sealed. What you'll notice the most is the hole spacing, beveling of the edge and every now and again the height (thickness). The new Hohner Rocket has noticeably larger holes than the Hohner Special 20. The standard Hohner Marine Band has a very slight beveling of the hole edges, with the Marine Band Deluxe and Crossover having a much more noticeable bevel (though most don't notice it as a "bevel"... they just note the smooth feel in their mouths). The comparable Sydel 1847 has both a bevel and scooping, which is much more noticeable, giving the feeling of larger holes. In the end, experiment to see what feels best in your mouth. The standard is the Hohner Marine Band Crossover these days, so use that model as your reference point.