Apple Cinema Display is one of the best monitors on the market. It has enormous resolution (2560x1440) and uses IPS panel (the best panel type) and LED backlight. Those cheap 22" monitor in Walmart have TN panels and lower resolutions.
50" TV is only 1080p, 27" ACD has more pixels. TV isn't the best external monitor unless it will be used mainly for watching videos. If you're going to use it for something else, get a cheap-ish 1080p monitor from any shop if you don't want the 27" ACD