Kryonet: Best way to send / read simple TCP messages?

I’m pretty new to all of this, please bear with me:
For most cases in my game, I register and send specific classes via kryonet which contain specific values (Attack.class has caster, target, dmg).

But for a number of use cases, all info that’s needed could either be the class itself (StartFight.class) or it could be a String “Start Fight”.
What are the pros and cons for either approach? I’d either have a long list of

if (object instanceof SomeSingleUseObjectWithNoVariables)
else if (object instanceof SomeOTHERSingleUseObjectWithNoVariables)

or of

if (object.equals(“Start Fight”))
else if (object.equals(“Exit Game”))

and so on. Is there an even better approach?

Many thanks!