I've visited the websites of all of the browsers you listed. All of them have the same-ish UI. I don't really know what a 'workspace browser' is so I don't have nearly as concrete of an opinion as someone that uses one of these daily. But, from the UI alone, they feel like the Opera web browser (they are definitely not the same, and probably serve different purposes but this is the impression I get). Does one of these browsers have more features? Which one do you feel comfortable using?
Also, unrelated, but can you or someone else explain to me what is a 'workspace browser'? What purpose does one of these serve?