Hi Terry,
Generally speaking, you'll find overall good reviews of the Downtube bikes. They will likely be a step up from the Citizen bikes you had before. I suggest doing a search on this forum for Downtube and you'll find several threads that talk about them.
You might also look at the Dahon line of bikes. They're quite popular, and there should be a couple of models in your price range.
Finally... I know you mentioned owning a Citizen before, and you might take a look at their current offerings as they've changed. You might find something there that you like.
Good luck!
--sam