Each one of these has its own use. Would you use fish sticks in conduit that has multiple bends? No, you would only use fish sticks in places like dropped ceiling and strait conduit that doesn’t exceed 3 yards. Fish sticks are made out of fiber glass, they have a little bit of play designed into them otherwise they will break.
Fish tape is the exact opposite of fish sticks, but at the same time you can use it for almost all of the same applications you can use fish sticks for as long as you have the patience. Normal applications for fish tape would be conduit with many bends or places where you have sharp bends.
Pull string is attached to a line after you have already pulled cable through the conduit so that you can pull more cable through the conduit without having to re-fish.