As above it would depend what you want it for but there are good deals on the dell site, it's either www.dell.com/deals, or www.dell.co.uk/deals, can't remember which
go stand in tesc or asda etc ... they should have some 'puter mags on the shelves
see what they recommend ....
(this is a bit of a generalisation) most manufacturers will offer pretty much the same options within a price range...
a wider screen results in a smaller HDD or a slower processor .... but ethel is right ... horses for courses ... if widescreen is important ... you'll get less of something else.
online is generally cheaper than from a shop (but the gap is quite small these days)
it's important to go to somewhere you can touch and feel the machine (even if you buy elsewhere)