Replies to this post have hit around the point of breaker sizing with some details left out. The point of the breaker is to protect the wiring, not the device (winch) at the end of the wire. Failure to protect the wiring can result in an overheated wire with the risk of fire, exploding battery, etc, in the case of a wire or winch short to ground or overloading an undersized wire.
The wire should be sized to deliver the current that the winch at the end of the wire demands keeping in mind the length of the wire run. Once the wire size for the device is determined the breaker is sized to protect the wiring.
Keeping that in mind, ensure that you do not place a smaller wire after the breaker for lights, etc. without adding a breaker or fuse to protect the smaller wire size.
Your winch documentation should define full load current. If not, one horsepower equates to 746 watts.
Watts in a DC circuit equate to voltage times current. Dividing 746 watts by 12volts yields approximately 62 amps for a 1 horsepower winch.
Simple search on 12 volts DC wire sizes will give you the wire size you need, somewhere between 4 and 2 gauge wiring depending on the length of the wire run. Then select your breaker to protect the wire for the current the wire can handle, in the example above, conservatively a 60 amp breaker should do the job.
I'm sure plenty people have sized wires smaller than this and are satisfied with their winch performance. Still fine as long as the breaker is sized to protect the smaller wire. For example, even though the winch requires 60 amps, smaller wire size is selected and can only handle 40 amps. The breaker then needs to be sized to the wire capacity, 40 amps and not the winch capacity, 60 amps.
Larger wires are better. Simple example is when you try to jump start a car with a cheap (small wire gauge) pair of jumper cables with no results. Someone then shows up with a more expensive (larger wire gauge) set and the car starts.
Any case, at the end of the day protect the wire size with an appropriately sized breaker for that wire. The standards are defined by the National Electric Code which is part of the NFPA, National Fire Prevention Association. Don't burn down that Pioneer!