DeMon, I bought a plasma in Feb after doing a bit of research.
Size: I was deciding between 42" and 50" but decided to go to 42" because it fits in perfectly in my TV alcove. The 50" would be too big for that space. The differential in price is about $1100 or so for the same brand.
Picture Quality: V. Important to me - After checking out a score of stores - Best Buy, Circuit City, Tweeters, Home Theatre Store, etc, I found that the Panasonic plasmas had the sharpest pictures. Truly stunning. I loved the Pioneer too but I thought it was overpriced. The Pioneer comes with a separate box where all the inputs are connected while in the Panasonic the cables are directly connected to the TV. I remember reading something some issue with the Pioneer box - either a bit of disturbance to the picture or some droning sound from it - I forget which.
What you should do is visit a variety of stores and check out the TVs on display - dont just check one type of store - say Best Buy because there could be any number of reasons why one TV shows up better than another (poor cable quality for instance). I am pretty sure you will be able to narrow it down to one or two TVs very quickly.
For me the Panasonic stood out (my model: Panasonic TH-42PX50U) and was reasonably priced - $2999.
There is a lot of info here on this site:
http://www.avsforum.com