A top end lcd should look great and a bottom end lcd will more than likely look crap. It's probably the same with plasma, but i've gotta say the one I bought last year looks absolutely stunning in both sd and hd for the main channels and I got lucky and found it for 500 quid. It's a Panasonic and only hd ready (as opposed to full hd) but I did my research first and found the reviews stating that sd signals looked amazing on it as well as hd, and given that the vast majority of broadcast programmes are still broadcast is sd, then I reckon that's the most important factor when choosing a tv for normal viewers
Most full hd sets i've seen look absolutely crap when watching standard definition programmes and some of those people don't even have the means to watch HD tv so they're watching shit tv for no special reason, so don't be seduced by the higher pixel count unless you read a good review about it - and that includes reading the bit about sd if you're going to be a normal viewer as well as a gamer
Regarding LED sets, they fall into 2 main categories. 1 of which is LED backlit - meaning that rather than having flourescent backlighting in the set, it used led which although uses lower power, it isn't a true led pixel tv, so it's worth checking the smallprint if you're wanting a led pixel tv
Do your research and look for award winning sets (mine had won loads of awards) or at least check out anything that looks like a bargain by searching google for information about that given model to see if customers are happy with theirs, or complaining about them
That's my advice anyway if anybody wants it