If in case you are not familiar with what these things are, these are known to be algorithms that are used to ensure that digitization will take place properly. If in case you are wondering, these were used for telephone algorithms in the past. One main difference is the input of these two. U law will offer a better dynamic range as compared to the law.
Dynamic range will refer to the sounds that can be produced by both. They can be quiet or loud. Another difference between U-law and A-law is they are being used in different countries. U-law is being used in North America, while A-law is a common thing to use in Europe.