I very much doubt that there will be much to choose between them in practice, although the Sony's 100Hz refresh rate might give it an edge with rapid motion. That isn't guaranteed, though, so I would recommend finding an example of each to look at before making a final decision. Another thing to consider is how they handle standard definition. At the moment there are only four HD channels on Freeview (five if you include the BBC's temporary Red Button service), so much of your viewing will still be SD. There will be more HD channels in time, but don't expect them immediately.
Years ago, sets in this area of the market frequently suffered from poor black levels, unsharp SD and sluggish motion handling, but I would say that the mainstream manufacturers (ie. Sony, Samsung, Panasonic, LG and Philips) have got all of those shortcomings pretty well licked now and you can pick up a very nice TV indeed for the sort of money you are considering. A greater outlay would buy you a bigger screen, 3D and ever more 'smart TV' bells and whistles. If all you want is a telly that isn't so big that it dominates your room, and will still deliver excellent pictures, however, I would think that either of them would fit the bill.
Final point. Be prepared to play around with the settings. The default set-up is designed to make them look enticing under shop conditions, which will almost certainly mean that the colours look way over the top in your home. Spend a few hours adjusting everything (preferably while alone) to get it looking just as you want it.