By default, the Graphics.DrawImage method scales Bitmaps efficiently but unattractively. To avoid ugly aliasing ("jaggies"), set the Graphics object's SmoothingMode, PixelOffsetMode, CompositingQuality, and InterpolationMode to high quality:

public static Bitmap Scale(Bitmap Bitmap, float ScaleFactorX, float ScaleFactorY)
{
    int scaleWidth  = (int)Math.Max(Bitmap.Width  * ScaleFactorX, 1.0f);
    int scaleHeight = (int)Math.Max(Bitmap.Height * ScaleFactorY, 1.0f);

    Bitmap scaledBitmap = new Bitmap(scaleWidth, scaleHeight);

    // Scale the bitmap in high quality mode.
    using (Graphics gr = Graphics.FromImage(scaledBitmap))
    {
        gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        gr.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
        gr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
        gr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

        gr.DrawImage(Bitmap, new Rectangle(0, 0, scaleWidth, scaleHeight), new Rectangle(0, 0, Bitmap.Width, Bitmap.Height), GraphicsUnit.Pixel);
    }

    // Copy original Bitmap's EXIF tags to new bitmap.
    foreach (PropertyItem propertyItem in Bitmap.PropertyItems)
    {
        scaledBitmap.SetPropertyItem(propertyItem);
    }

    return scaledBitmap;
}