Firstly, lets explain what Freesat & Freeview are, & what they both have to offer.
In August 2013 it had some 60 DVB-T TV channels, 26 digital radio channels, 4 HD channels, 6 text services, 11 streamed channels, and 1 interactive channel. Some ten additional feeds, whereof five more HD feeds, are expected for the first half of 2014, and up to 10 new HD channels are planned to be launched later in 2014, from a new group of multiplexes awarded to Arqiva. The new HD channels were launched in selected areas on 10 December 2013 with a further rollout expected during 2014. Wikipedia
FREESAT is a Free to Air Satellite service and you have to have a satellite dish installed on your property to be able to receive this service. It has a very similar channel list to that of Freeview, but on the whole it has more TV channels. To be able to watch it o your TV it will need a Freesat receiver for each TV (unless it has a built in receiver). This ends up more costly than the freeview option.
Having had both of these services I can say that if it was me choosing, for the cost and practicability of it I'd choose Freeview as it has most of the channels I watch and the extra channels you get with Freesat are in my opinion poor.