Its hard to say, but ive got vintagecomputer.co.uk but would have prefered vintagecomputers.co.uk (but this had already gone)
I suppose it really depends on the website your building.
toys.co.uk is better than toy.co.uk for a toy shop
shop.co.uk is better than shops.co.uk for a general shop.
If its a brand name then you dont really want a plural, if its a name based on what you are selling then a plural is better.
game.co.uk is more of a brand name rather than a description of what they sell... even though they do sell games... if they hadnt advertised there brand then they would have been much better off getting games.co.uk
Thats my view on it anyway.