Darwin, yeah, I guess you know then!
I think the real, bottom line, determining factor for me in this category of software is the software's ability to work with NON-standard dialogs. However, none of the programs work with non-standard dialogs. And they all pretty much work with the standard dialogs + Office dialogs.
File-Ex had a great idea with the "training" of new dialogs, but the truth is that it still doesn't work with any non-standard dialogs. All that happens is that you train a new dialog, and the File-Ex interface will pop up for that dialog later, but when you choose the folders and stuff, it still won't work right. So, it only seems to work right. Same for Filebox extender, like I mentioned before. The buttons may appear on the non-standard dialogs leading you to believe that it works, but when you use the buttons, it doesn't work.
Therefore, the only factor that a user should use to help them choose is really interface, that's pretty much it. For me, I like the Direct Folders interface the best.
Hey! Darwin, and Tomos, I used to have Powerdesk also! Yeah, I remember their dialog helper, it was pretty cool at the time. Nothing special, but it worked as well as the others that are mentioned here. Powerdesk was a cool suite. I used it from about 1998 until 2004, when I started learning more about other software out there...Dopus and such. But before I was a hardcore poweruser, Powerdesk was awesome!