I own both DeWalt and Milwaukee potable powered hand tools.
We all have our personal preferences when it comes to powered hand tools. I know this thread is about portable power tools but when it comes to corded 120V tools I think Milwaukee power tools are the best. Although I have a DeWalt table saw and Rigid shop vacs. All great products. I have no first hand experience with Ryobi or Makita.
When comparing performance, apples to apples, ie. 12v to 12v, 18v to 18v, or equal 120v HP, etc., I doubt there is much difference between them all.