Keep a few things in mind. First, HDTV has 2 forms, 1920x1080i and 1280x720P. We are not going to get 1080P which is true HD. Also 1080i really doesn't exist as a displays resolution as the set either has 1080 pixel rows or it does not.
That said, NO plasma screen produced today that is 42" or less is an HD of either type. They are almost all 1024x768 panels meening they are a stretched XGA machine.
Plasma's largest down fall is the glare. Its bad, sometimes REALLY bad. If you are considering placing a TV facing an open window or a light, then plasma may be a problem.
LCD and DLP tvs are going to need a $350 lamp swap every 2-3 years. The nice part is that unlike plasma which dims over time, once the bulb is swapped, the TV is back to its original brightness. The major pain to me about projection TVs is the wait time for them to warm up. Its usualy 20 seconds or so. being only 12" or less thick, they are easy to place.
For DLP projection TV's, technicly they are not really ever HD becuase only one color is on the screen and any moment. Of coarse this is also happening so fast most no one can detect it. I am not sure wether DLp has ever reached 1080p like LCD sets have. I have yet to see the DPL projector I liked so I guess I can't reccomend them.
LCD panel tvs have some major advantages, 1st is that they can have as high a resolution as the projection TVs. Also they dont need bulb raplacments and they are VERY lite compared to a plasma screen. There down side is that LCD just doesn't have the fluidness of a plasma or of a CRT. Simply put, pixilation is easy to detect in rapid motion scenes. For the 42" size, LCDs are still price compeditive with plasma, after that however, the costs favor plasma heavily for 50-65" sets.
In all, its completely TV by TV. There is no hard and fast rule as there are alot of other electronics in sets then just the light source. You should check them all out and see which you like the best.
At home i prefer plasma, and an angled wall bracket can help with the glare. But for my company (
www.singlesourcegroup.com) where I am an audio/visual integrator, I almost always use LCDs since most of the displays are running computer graphics or atleast have to operate in moderate to high light environments where no one ever took the glare off of a display into account when laying out the lighting plan.