Unity by default will choose the constructor with the most parameters. If you want it to use a certain constructor when you're register the mapping, you can use InjectionConstructor.
// Using default constructor
this.unityContainer.RegisterType<ILogger, NLogger>(new InjectionConstructor());
// Using ISomeService constructor
this.unityContainer.RegisterType<ILogger, NLogger>(new InjectionConstructor(new ResolvedParameter<ISomeService>()));