Logically speaking, beyond placing the field replicated in subclasses vs. in the base class, there is a third option which is to introduce a subclass that has the common properties between the two.  @Pete hints at this without fully going there.

Using @Pete's example, we would introduce a (possibly abstract) subclass for Wheeled Vehicle that descends from the original base class — while the two subclasses descend from it.  Thus, the original base class is not polluted with wheels, yet the commonality of wheels is DRY (not repeated among subclasses that have wheels).

This may, of course, be overkill for your purposes, but such is supported by the class hierarchy mechanism.

Logically speaking, beyond placing the field replicated in subclasses vs. in common in the base class, there is a third option: which is to introduce a new subclass into the hierarchy that has the common properties between the two.  @Pete hints at this without fully going there.

Using @Pete's example, we would introduce a (possibly abstract) subclass for Wheeled Vehicle that descends from the original base class — while the two subclasses descend from it.  Thus, the original base class is not polluted with wheels, yet the commonality of wheels is DRY (not repeated among subclasses that have wheels).

This may, of course, be overkill for your purposes, but such is supported by the class hierarchy mechanism.