The best merchant ship for a nuclear-power demonstrator

What civilian ship type would make the best proof of concept for renewed nuclear merchant propulsion?

An ultra-large crude carrier or large gas carrier that spends most of its time underway and seldom enters port.

An ultra-large crude carrier is the preferred example because it could remain offshore, discharge its cargo, and continue along a regular route. A large gas carrier is suggested for similar reasons. Both examples favor a ship that spends much of its time moving and enters port infrequently. This operating pattern reduces the importance of finding frequent port calls that will accept a nuclear-powered merchant vessel.