Which is a better pattern for dependency injection when you also want a "default" concrete dependency?

I've used both of the below patterns for testability and I'm wondering which is better OOP/SOLID.

Pattern 1: Provide two constructors, one of which creates the concrete dependency

public MyClass
{
    private IDependency dependency;

    public MyClass() : this(new ConcreteDependency()) { }

    public MyClass(IDependency dependency)
    {
       this.dependency = dependency;
    }
}

Pattern 2: Base class has dependency intializeer and derived class calls it with concrete dependency

public abstract MyClassBase
{
    private IDependency dependency;

    protected void Initialize(IDependency dependency)
    {
        this.dependency = dependency;
    }
}


public MyClass : MyClassBase
{
    public MyClass()
    {
       Initialize(new ConcreteDependency());
    }
}