We have an LCD in our bedroom and a plasma in our basement family room. I know they say plasma is better in low light, its surface is more like a glossy finish picture and is prone to glaring from sunlight or bright room light. The LCD screen is more like a matte finish picture and works better in bright light.
We have had our plasma for almost two years, and a wii hooked up to it. We have not had any problems with images getting etched in. We also have children ages 1-9 that use the TV a lot for movies, shows, wii, etc, and they do get smudges on the screen, but it cleans easily with the soft cloth and spray that came with it, no damage to speak of.
I was worried about energy usage, I had heard that plasmas were the "gas-guzzlers" or TVs, but ours is labeled as EnergyStar (not sure what it takes to qualify for that), but we have not noticed any big changes in our electric bill since getting it, and as I mentioned it gets used A LOT!.
I do think the colors and picture quality is better on the plasma, esp HD, but I am not real picky when it comes to that. It was my husband that insisted the plasma image was better quality and worth the cost (he is a bit of a movie buff and wants them to look as good as possible).
I think our bedroom one is maybe 37"ish, can't really remember, but bigger than I had wanted for the bedroom (again husband got the final call on that). Our plasma in the basement is HUGE, I am pretty sure >50", when it was delivered it thought it was embarrassing large, but i have gotten used to it. It is in a large open space, so I think that helps. Consider the space you will put it in, how close or far you will sit from it. Somewhere I read some general guidelines for best viewing distance related to size of TV. Here is a link to one site that discusses this:
http://www.crutchfield.com/S-V4q3Ki4fRvU/learn/learningce...
That may help with your decision. Maybe even cut some cardboard or something to the sizes you are considering to see how the size looks in the space.