Plasma is definitely the better of the two but think carefully before you part with you money.
The life of both types of screen is notably less than a conventional cathode ray tube and a plasma screen has a shorter life than TFT on average.
We have a couple of large plasma screen in the studio here for presentations and I took one home a few months ago to try it as a television (it is equipped with a tuner). I can't explain why but after watching for about two hours I noticed I was getting a sort of "viewing fatigue" and eyestrain. This may just be me but, see if you can get one on trial and see if you get the same..
TFT screens have a limited viewing angle and I just can't get on with them at all. Even though several of my staff wouldn't use anything else now, I still stick with my 19 inch CRT on my computer.