Which one would you pick for cutting belt/line/rope/fabric etc.? From the pics the v cutter looks like it cannot be sharpened so that's no good. Serrated line cutter seems to be the best out of the three.
Scissors cut paper / cloth / etc.
V cutter cuts seatbelts, webbing, etc
SLC cuts anything else - including line, wire, insulation ( limited to size of the item being cut.)
Look at the
Spyderco Triangle Sharpmaker for ALL your sharpening needs ......
For more detailed work look at the
Spyderco Ceramic File Set small sharpening stones, they will sharpen a "V" cutter.
More sharpening info here