I think it comes down to personal tastes.
Plasma's imo reproduce a better picture than lcd hands down. They still do somewhat suffer from "burn in" if left on for hours and hours and hours on a picture that has a static logo that is bright, but they have gotten better by pixel shifting the entire image to avoid this, it's not that big of a deal anymore. Plasma's do have a fairly reflective front coating on the glass which doesn't do too well in highly bright areas, like lots of windows and do use more energy and can become great little heaters in the winter.
LCD's have gotten better, but imo, they all still suffer from how quick the lcd pixel can shift from state to state. Most approach around 5ms or less, but in complex scene's I still can see alot of pixelization, but some sets handle this better than others, again..personal preference and you get what you pay for.
One thing that has been affecting both Plasma and LCD's are the quality of the capacitors they are using in the set, and I've seen more LCD's croak after 2 years than plasma's. I think thats because the plasma's run a little warmer, they have been using better quality components. Personally I don't like Vizio's. They look great, but they don't last and good luck getting support out of them. They will funnel you to "their" repair depots to get fixed, and they will not even let you buy schematics or replacement boards. Thankfully their have been enough people parting out vizio sets on E-Bay to get parts.
I would also caution buying from Walmart because they have beat up the supplier so bad on price, that the ones sold to Walmart usally are lower quality units or off model numbers with less features specific to Walmart. Have also seen units that are several years old being sold as new, 2009 models being sold as 2011.
The one thing that you should do is always make sure the set is plugged into a surge suppressor at a minimum. This will help the switching power supplies in these sets last alot longer, they don't like AC voltage spikes that will occur from your local power utility.
Steve