Like most desks-with-chairs, the ideal work environment is going to be unique to the person and to the task.
I find writing with a paper and pen or typing for less than a few minutes at a time easier to do if I don't have to change my standing or sitting mode. I find doing the same for between a few minutes and about half an hour somewhat easier to do sitting down than standing. If I'm writing or typing more than half an hour I'm probably going to take a break anyways.
I find it uncomfortable to stand more than 6-8 hours a day or more than 1-2 hours without a 20-30 minute sit-down break, but that's just me. When I was in better physical shape (read: when I was a teenager), I could do stand-up work in a restaurant all day with just a sit-down break for meals.
As far as which stand-up desk/workstation will work best for me? I'm not sure. Given my current job requirements, I doubt any would be as good as an ordinary adjustable sit-down office chair and a typical office computer desk. I'm almost certain your job requirements are not exactly the same as mine so your ideal work environment will very likely be different as well.