I have an old Chicago Cutlery 8" fillet knife.  It has a wider blade than most traditional fillet knives but still fairly flexible.  It also does not have much curve to the blade.  It has a wood handle which is not as slick as plastic when wet.  
I try and keep it sharp enough to shave the hair off the arm.  Best way to keep it that sharp..., keep it away from Mrs. fishinbuddy, she never steels the knives when she is done.
Good carbon steel, sharpens well and holds an edge and only needs to be touched up with a fine steel after each use.  
I used to work in a restuarant and have tried all sorts, never found one I like as well.