While buying a plasma or LCD television is actually a subjective thing, I have some personal tips that might come in handy :

• The minimal distance between the television and the viewer should be 4 times the screen size, so if you have a 42 '' screen which equals about a metre, your viewing distance should at least be 4 metres. If you are sitting any closer, it feels like you are sitting in a front row seat in your local video theatre. This might be fun in the beginning, but it tends to get quite exhausting when looking from such a small distance for a longer time. 
• If you have analog cable-tv, make sure to get a cable signal amplifier, because a bigger screen estate also needs a higher quality signal in order to be enjoyable.
• If you have a partner, try to get his/her opinion as well, since it probably is dominating (a small part from) your interior.
• If you have the possibility to choose for a seperate higher end speaker system instead of the standard not-very-high-fidelity built-in speakers, please do so, since it is the whole package that makes your experience more immersive.
• Finally, make sure it stays practical, for example : for me the ideal height to hang the screen would have been about 60 centimeters from the ground, but since we are expecting a child, I have chosen to hang it a little bit higher, so it is impossible for a toddler to reach for it, and do some damage. 

Good luck !!!