3D printing nozzle characteristics

Nozzle shapes and nozzle materials

Obviously the nozzle diameter is one of the major parameters when 3D printing. But you may have wondered about the many nozzle shapes that are available on the market. Some brands have preferred shapes. And, even though will not have a drastic impact on the print, they may be significant and worth a post.

Overall length of the nozzle?

Marketbot vs Ultimaker nozzles.
Both are quite long, but the former has a
bigger flat ring around the nozzle hole.

In my opinion, long nozzles are more convenient for cleaning, and they let more cooling air flow around.

Shorter nozzles reduce heat loss a bit and they probably give a better control and reading of the temperature (remember: the sensor is on the heating block, not on the output).
They could arguably help to reduce the overall length of the hot end, so they reduce could positioning error slightly. And they may spare a few grams... But this is marginal and for the most hard core players: they will not help make a bad design better!