In my opinion it is hard to beat the value that the established brands, such as Brompton, Bike Friday, Birdy or Dahon, provide. Folders are in many ways more tricky than regular bikes and you generally get ironing out of all kinds of problems that can occur. Yes, you can improve upon them, see e.g.
Jipe 's post, but at least you have a fine working bike that you can use in the meantime. Which bike to start from depends on personal circumstances including how you want to use the bike and the funds you can delegate.