I voted Dopus. Thats what I use most. However I can see a clear advantage of ABC-Dir in the screenshot. Because it has the buttons in the middel it uses up more space in width. While dopus having buttons below the filelists it uses up more space in the height. Therfore ABC-Dir might have the edge when 640x256 is the maximum screen realestate.
Actually ABCdir doesn't use up more width, it just uses a smaller font. It is actually 640x425 in my screenshot (unfortunately the width is fixed). But it's not just about size. Having 2 rows of small buttons in the middle means you have to move the mouse less distance to do everything (not up & down the whole time). And the volume buttons over the list windows is nice too.
I don't know if anyone noticed but that block above the middle buttons is a "scroller" that allows you to flip to the next page of middle buttons - so you can define as many as you want and flip (I defined 2 "pages" of buttons). And you can copy in either direction - left list to right or right to left. You can even define 2 actions for each filetype - one on doubleclick, one on left-right click.
I don't mean this to be an advertisement for ABCdir, but I love it.
If there's something better, I definitely want to get it.