The answer varies depending on the desired finish, location and application of the walk (residential, commercial, industrial etc.)
Most frequently I’ve concrete with:
Latex sealants which typically provide a “wet” natural concrete look. This may be the best for you if you don’t mind the wet look. It will have to be re-applied every few years to keep looking fresh.
2-Part epoxies, which typically come in grey or white but can be tinted to a desired color. These are better for garages, industrial kitchens, and anywhere you don’t want oils or grease to permeate the concrete.
Regardless, of your chosen sealant be sure to either apply to relatively new concrete, or use a good stripper/acid/concrete cleaner prior to applying the sealant. Be careful as all these products are very caustic and can cause blindness, burns, and/or asphyxiation.
If the concrete is stained, as stamped concrete often is, be sure to test a small area with the cleaner/stripper to insure no loss of pigment or damage to the stain.
As always read the manufacturer’s warning labels which are provided with or on the container. It will give you an idea of what to avoid and the best practices regarding application.