close or dispose

The using block will call Dispose() on the StreamReader instance. Generally speaking, if a type is IDisposable, you should put it in using scope.

EDIT:
If you look at the Close() implementation of StreamReader using Reflector, you will see that it’s calling Dispose(true). So if you’re not using the using scope, calling Close() manually would be the same as calling Dispose() in this particular case.

protected override void Dispose(bool disposing)
{
    try
    {
        if ((this.Closable && disposing) && (this.stream != null))
        {
            this.stream.Close();
        }
    }
    finally
    {
        if (this.Closable && (this.stream != null))
        {
            this.stream = null;
            this.encoding = null;
            this.decoder = null;
            this.byteBuffer = null;
            this.charBuffer = null;
            this.charPos = 0;
            this.charLen = 0;
            base.Dispose(disposing);
        }
    }
}