Determining the paint system you are going to use on your boat, really comes down to considering these factors: time, effort, and budget.

One-part paints
Traditional one-part paint (or alkyd enamel) can be applied ‘straight from the can’. This product will dry reasonably fast by solvent evaporation and/or by reacting with oxygen or moisture in the air. It’s easy to apply and has very good weathering characteristics. The alkyd (oil resin base) can be modified for gloss, hardness or longevity by using additives.
More alkyd enamels are still used than any other type as excellent finishes can be obtained from them with a minimum amount of effort.

Two-part paints
Two-part aliphatic polyurethanes are obtained by mixing two components according to a given ratio. Those parts start a chemical reaction that forms a chemically cured surface. Once the two parts are mixed, you can only use it for a set amount of time.
In comparison, two-part products dry quicker and have better properties: gloss, color retention, hardness, longevity, chemical and abrasion resistance, and overall film integrity as you vary the chemistry.