I bought the 3rd gen on my last trip to Vegas for ~ £320. Was slighty gutted it was the 'latest' iPad for only a month (thanks Apple!). Although the 4th gen is not much of an upgrade. I have the 16GB wifi. I don't need the celular one, just tether it to my Galaxy S2 if I need to use it while out and about
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I find I am using it all the time. Don't enjoy browsing on my phone anymore! Great for watching iplayer or movies in the lunch break
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You may as well go for the latest as the older ones don't sell for much less.