If you are talking about tile showers, Depends on the application. Schluter products (orange) have great flexiblity in a variety of applications. Especially for barrier free showers. Better to use the complete system when using Schluter.
I second the earlier answer. Higher material cost is well worth using the Schluter underlayment It can save in labor/time, it is a superior product to most out there and there varied solutions help insure you find a fit for all size and shaped bathrooms. Its all we use now and they have great built in heated floor solutions that are safe to use in wet areas.
Since I do things the old way I use Mapei Aqua Defense or Laticrete Hydro-Ban for the most part. Another good product when waterproofing pools, fountains, or Mikva’s is Aqua Fin 2K
The Schulter system is the best for all wet areas. The roll on system can be used for walls, I would not use for floors.
The Schluter Products is the way to go.