I know the 2109 is a excellent machine for its age, i brought my sister a 220E, and used components and svhs leads, and found it pretty much the same as my 2109.
Toshiba make excellent players, just check for a review of both players on a website like www.homecinemachoice.com, etc
The SD100 was brought out to replace the 2109, and supposedly improves on it. It's definitely not a cheaper version of the latter. I haven't done a side-by-side comparison of the 2 machines, but I can tell you that the SD100 gives absolutely superb picture quality on my Tosh RPTV.