One is called YKK Nylon and the other is a metal zipper with embedded rubber for seal. The zippers need to be left in the open position when the suit is not being used, including the relief zipper if you have one. The zipper eventually loses its seal because it was left in its compressed state and cannot expand to maintain a seal when zipped. This condition can also make the zippers difficult to open. The most frequent cause of zipper leakage is due to an incompletely closed zipper.
Zippers can also leak due to sand, grit or salt crust sitting in the zipper surfaces.
So, rinse them well after use. Use care when zipping in cold conditions. Clean and lubricate the teeth occasionally with paraffin, beeswax or a zipper lube. A dab of Vaseline at the closing end of the zipper will also improve the seal. There are a few materials I have had experience with for the shell of a drysuit or drytop.