Sky

What is the difference and which is better?

Freeview is terrestrial so is picked up via an aerial. Freesat is satelite, so you need a dish. There are more channels on Freesat than freeview, but they are NOT the same channels. on freeview you get stuff like dave and ther UKTV stations, among others. On freesat you get the Zone brand of channels, some more news ones, and more shopping. Freesat has HD already, so you can watch BBCHD and ITV HD (but you need a HD box to get this, they do normal ones too).
the main advantage of freesat is coverage, as terrestrial is affected by geography not everywhere will get it (not that this will stop the gov’t turning off analogue!) so freesat is only not availble to people who cant put a satelite up pointing to the sky in the right direction (maybe because of a large buildingor mountain). if you check out their respective sites you can see a full list of channels.
it should also be noted, for ease of use, that freeviews channels are numbered 1,2,3 etc, whereas freesat is numbered 101,102,103. (we bought freesat for my granmother due to geography, but as she is partially sighted we checked the channel numbers, but they lied to us)
another thing to note is the potential availability of iplayer, they will soon be putting it onto HD boxes and then later next yr all boxes should get it.
the other major difference is of course the price, it costs around £80 to get a satelite dish installed, plus £50 for a basic box, whereas freeview boxes start at about £15.