The difference between chossing if you are to get an LCD or a plasma should boil down to the type of room you are going to put it in or the viewing angle.
If you have a darker room with not many light sources entering such as windows, go with the plasma. The colors will show a lot better than an LCD. Plasma screens will show glares, so the LCD would be a good choice if you're dealing with that. Also, LCD can be viewed from the side at better angles, so if your seating is not ideal an LCD would be a good option.
As for life of a tv, they have become close to equal in the later models. One of the early turnoffs was the burned image. This has been fixed in recent plasma's as they now have circualting gas chambers, creating a very low chance of ever having this happen. Just double check that it has that technology on it.
When looking for the quality output on it, 1080p is the highest, but Vizio doesn't support that high of resolution last time I checked, I could be wrong. 480i is what regular cable tv is broadcasted in, that is your base. (480 individual (i) lines of picture) 720 starts your high def. picture, 720 lines of individual or "scan" (progressive scan I believe, or 720p). then you get 1080 in both i or p. Note, 720p and 1080i is about the same, but 1080p you will notice some difference with the right components, as you will need either blue-ray or HD DVD format to really see the difference.
Also, make sure you check the prcessor on the TV, 120mhz is what I have so that shadow images don't show up when I use an xbox 360.
Vizio is a good brand for the price. Granted you won't get all the features of a highend tv, but for the price they are definately a good deal. Just make sure ahead of time that it matches what your current or future plans are for your entertainment system. Make sure you have all the outputs you want or need. Then, go with the biggest size that proportionally fits your space and in your wallet.
Another good place to check is Sears for tv's, I got a 52" Samsung 1080i plasma for $1499, about $400 cheaper than Bestbuy for the EXACT same model.