It needs to be cost effective (which might include profotabilit6), be feasible to implement, sustainable, and a bunch of other stuff too.
Aircraft carriers and subs being the only transportationethod using nuclear is a good sign that it isn't practical for shipping. That is likely a combination of nuclear requiring highly trained staff that are not just out in the work force, the ability to procure a reactor and maintenance parts, the ability to obtain fissible material, the ability to dry dock a ship with a nuclear reactor, and a bunch of other stuff that could even be affordable without being practical for reasons beyond costs.
Best depends on many factors beyond things like efficiency, weight, or durability. Lateen sails are easy to implement with a single mast, are easy to store and maintain, and everyone that has sailed has experience with them. Other sails might do a better job of catching the wind, but with tradeoffs on maintenance and usability.
Practicality is often complex and leans towards easier maintenance and established knowledge.