- I am not convinced that plasma is worth the extra cost. LED is fine.
LED is superior to plasma IMO.
- We have basic cable, will continue with basic cable when we switch.
What you need are high definition digital signals. Your basic cable has analog signals needed for your old TV, but somewhere it also carries digitial signals, at least for broadcast TV. An over the air antenna can also bring down HD digital signals for broadcast stations. Don't let the cable company tell you you have to get a "digital package."
- We're not huge TV watchers but we'd like to have something decent for when we do watch TV. And right now we watch all movies on the computer. (21-inch screen.)
If you spend the money for a 42" TV, you should watch your movies on it. You can likely port your computer signal to your TV. Look at the TV before you buy to see if it has a computer connection into it.
- One thing I'm not sure about is HD. Yes? No? I think yes with the option of no (the Viera is very adjustable) rather than no at all, but I'm not sure.
YES. Get a 1080p TV unless someone offers you an insane deal on a 720p. Analog starts to look horrible as you get bigger. You are not going to want to watch an analog signal on a 42" TV.
Panasonic seems to get good reviews.
That's probably fine. Samsung seems to get the best reviews from Consumer Reports.
So, any thoughts? Reasons I should get some other kind of TV? Bigger? Smaller? Should I go for this one?
TV size is really a function of budget and room size. If you are sitting around ten feet from your TV, 42" is fine. If you are more like 15", then 42" will still work but you could do more. Based on what you started with, I think 42" will make you happy.