Hmm...
All three of the monitors you mention are "pure flat" so that is definitely good.
The KDS AV-195TF's uses Sony's FD Trinitron aperture grill tube and has excellent picture quality and quite a good price, but I've had very bad luck with them as I've had to RMA my AV-195TF monitor 2 times in the 1 year I've owned it, both monitors went bad after about 5-6 months of use.
I've never owned a Samsung but from what I've heard on the forums people like them very much; the 900NF is especially popular here. The 900NF is a Mitsubishi Diamondtron aperture grill tube which, IMO, is just as good as the Trinitrons. I recently purchased an NEC 19 inch Diamondtron and it has been perfect.
The 955DF uses a more classic shadow mask tube instead of aperture grille. It's generally agreed upon that the aperture grilles have better quality in terms of brightness and vividness of colors - better for graphics and imaging, but the shadow masks are a much better value as you'll usually pay $100 more for a 19 inch aperture grille. Many also say they prefer shadow mask for text and general apps.
I would suggest that if your on a real tight budget, the 955DF would be just fine. But if you have a little extra to spend, you'll definitely appreciate Diamondtron or Trinitron tube so I would go with the 900NF. Hope that helps.