Are you capped at £1k?
If so I would walk away from ideas of the Brompton, there are two many parts that want swapping out/upgrading to get a decent bike at the far end.
In terms of bikes that are better to ride for the price you will of course be sacrificing the better folded package of the Brompton but look into the 'hons. There's one for every occasion* and they ride better than the Brommies £ for £ spent.
Why does it need to be a folder? Is it for the packaged size? For taking on rush hour trains**? For fitting into the boot of the car? Folding is a compromise on a bicycle, work out how much you need, would, say, the folding limitations of some of the 26" wheeled folders be acceptable?
*gearing and kit permutations are wide.
**check the train co rules carefully