There are not a lot of differences to consider when choosing between a liquid or powder detergent. Liquid detergent tends to be more expensive, which is a lot of peoples first consideration. Also, liquid detergent can be used as a stain pre-treatment, which is an advantage you wouldn’t have with a powdered soap. Some people believe that the powder dissolves slower, and ends up leaving a residue on your laundry. This may have been true at one point but most modern detergent powders have been made to dissolve quickly with virtually no chance of leftover soap.