Resolution
The major difference between widescreen computer monitors and HDTVs is the ratio of the displays. The Xbox 360 VGA adapter natively supports the 16:10 resolutions common to HDTVs, such as 1680x1050 and 1440x900 for monitors from 17 to 22 inches. The two HDTV resolutions are 16:9 ratio: 1280x720 and 1920x1080. Recently, computer monitor manufacturers have adopted the 16:9 format due to the common adoption of HDMI.
Type of Display
The VGA connector on computers is no longer the preferred method of connecting to a monitor. DVI and HDMI were developed specifically for LCD displays, resulting in a crisp, clear image. Since VGA was meant for cathode ray tube (CRT) displays, such as standard definition televisions (SDTVs) and older monitors, HDMI will look better in most cases, whether on an LCD monitor or plasma TV.
Audio
The HDMI standard was designed to carry both video and audio, so only one cord is necessary to output a complete signal to a display with speakers. The Xbox 360 VGA cord comes with audio RCA cables to connect to the display. However, for enthusiasts with audio receivers, a separate input, such as an optical cable, is usually necessary to output to a receiver.
Cost
Since the Xbox 360 VGA cable is a proprietary cable, it can be sold for a premium because there are only a few manufacturers of this device. The cost of this cable can be up to $35 new and perhaps somewhat cheaper used. However, the HDMI cable is a universal type, used on many different devices and can be purchased from a manufacturer other than Microsoft for between $5 and $20.