Most corded multi speed clippers are going to have faster spm (powerful). They will run quieter and are lighter in weight than cordless clippers. They can handle every variety of coat and difficulty level with less hand fatigue.
Cordless clippers are great for flexibility in moving around the dog or the salon without a cord. They are ideal for working in mobile salons or house call grooming where cords can be an issue. They are powerful enough to accomplish most grooming tasks. You also reduce liability of tripping hazards with cordless.