If you only criteria for a soap is slickness, there are hundreds of options. Essentially every shaving soap and even bath soaps like Yardley of London or Irish Spring are slick enough for shaving. Inexpensive shave creams like Cremo are quite slick when mixed with the right amount of water. It is only when you start looking for other properties in your shaving soaps that the field begins to narrow.
Generally, as you add water to a soap, the slickness of the soap will improve. However, as you add water, the layer of cushion/protection left on your skin by the soap will start to get thinner. When hydrating a soap, you need to add the amount of water that will provide the proper balance of slickness and cushion for your skin. Some people like their lather on the dryer side to provide more cushion. Some people like their lather on the wetter side to provide more slickness at the sacrifice of cushion.
The best shaving soaps today are easy to load onto your brush, easy to develop a smooth lather, provide excellent primary slickness and excellent residual slickness (the slickness that remains on your skin after the blade has scraped off the visible lather), provide excellent cushion/protection to provide an irritation-free shave, and provide post-shave moisturizing and conditioning to keep your face feeling soft, smooth, supple and moist for hours. You may or may not be interested in all of those properties depending upon your type of skin and your shaving routine.
Soaps and creams are available over a wide range of prices. However, price is not always the best indicator of quality. There are some inexpensive soaps that perform reasonably well. There are some expensive soaps whose performance falls short of expectations.
Some of the best soaps today are made by: Ariana and Evans, Barrister & Mann, Declaration Grooming, Gentleman's Nod, Grooming Department, Highland Springs Soap Company, Hub City Soap Company, Murphy & McNeil, Talbot Shaving, Wholly Kaw, and Zingari Man. However, there are many other traditional and artisan soapmakers who make excellent soaps and creams. I have tried about 180 different soaps representing 90 different soap formulations. I can get a decent shave using any of them, but only half of them will give me a great shave.
Dominicr of Sir Henry Sundries/Black Tie Razor Company mentioned a soap that he sells. I have not used the soap, so I cannot compare it to the soaps I listed. However, looking at the list of ingredients, it should be a very good soap that sells at a reasonable price.
