This is entirely opinion, I might think xfe is best, and for me it is, but George says Thunar is best, and Bryan says MC is best,... and then Joe, just does everything from a terminal emulator, he says xfce-4 is best,...I suppose the best method to determine which file manager is best is to try various ones, and then decide which one you feel is best. What do you mean "powerfull" GUI ? generally the more bells and whistles a GUI has, the more useless it becomes, but that is just my opinion,... Ahh, Lynx is a excellent browser, but also makes a great file manager,...
http://nixnik.50webs.com/lynx/00_main.html