Don't suppose it really matters. I leave mine on the mains switch. However my new LG 28" W/S TV which uses just a two wire connection to the plug. i.e. mains live and neutral (NO EARTH WIRE) states that it is advisable to remove the mains plug overnight when TV is not in use. Take your choice. To be really safe. Switch it off at the mains.
Any manufacturer is likely to advise unplugging the equipment when it's not in use. That way they hope to avoid being sued in the unlikely event that the equipment blows up, burns the house down and kills the occupants! Modern equipment, computers included, generally aren't completely switched off when powered down, but instead are put into a standby mode. Because of this, failure of a component can cause a fire, with the potential to result in the consequences I described. The fact that this is very unlikely to happen doesn't mean it can't. Most of us happily leave our televisions etc. in standby mode, but only a very foolish person would risk litigation by saying that this is good practice.
You could also buy a Surge Protecter. This way your covered always. You may even got a couple of new PC's out of it if anything goes wrong with the s/protecter. You've got two types of insurance this way.
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