Couple of good points above.
LCD are in two varieties (actually three now). Basically a rear projection model (but much thinner than days of yore--think 12-24 inches) which will last longer than the flat panel lcd but have a narrower field of view (but again, greatly improved).
Of the projection variety, they break down into a larger size LCD projected versus an LCD "chip" that is projected. That later variety is thinner (on the 12 inch side of the scale) and runs "cooler", so the pixels should last longer. Also, when the end of the chip's life nears, it's supposed to cost less to "pop in" a new chip. Of course, they cost more up front. The flat panel variety of LCD have a shorter life span, and I think it's based on heating issues, but are truly "flat", meaning thin, and have a broader viewing angle. Also, if you go for a large size, flat LCD will actually surpass plasma in cost.
Plasma's biggest drawback, other than buy-in price, is the risk of burn in. If you are anticipating using it at all hooked up to a computer or a game console, don't buy one. And based on the post above, even leaving it on a fairly static "frame" such as CNN may eventually cause burn in.
We have plasma, don't play games on it, and certainly watch CNN and the like, but don't leave the television on those types of channels all day and night.
Personally, plasma met our criteria of best picture quality (subjective), broadest viewing angle (even better than tube), resonable cost for the size we wanted, and projected longest life. For us, hooking up a gaming unit wasn't even a consideration.
So. To some up in a few words?
1. Decide on gaming or computer use of the screen.
2. Decide what's the smallest size you will truly be happy with.
3. And move around while viewing any of the models.
There is no global "right choice", in the end you'll have to test drive them all.
