Jarvis and the others are just different methods for how the dots are distributed. As you choose different dither methods, you’ll see a brief description under the preview.
The important things are:
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Dot size: With an 80w CO2, your smallest dot is going to be around 0.15mm or a little larger, though it depends on tube, mirror, and lens quality. Don’t try to engrave an image with an interval of 0.05mm because you’ll just bleed your dots together and lose the white areas between dots.
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Material: different materials darken and vaporize differently. Wood has grain, and areas with dark grain tend to darken faster. Basswood and Alder tend to darken well, and have light grain. Birch is cheap, but doesn’t hold as much contrast. Pine is highly variable. Don’t use crap wood if you ultimately want to engrave on anodized aluminum, because the settings will be completely different.
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Power: small differences in power can make a big difference in output, so run small test swatches to see what works.
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Speed: PSU’s have a response time. If you go really fast, and make small dots, the PSU might not fire fast enough to actually fire the tube, so you’ll miss subtle shading. At high power/speed, material tends to vaporize before it darkens. Slow down, and use less power, to get better contrast. Defocusing a touch can help too.