As rusky says. Although I suspect you would only really notice a difference on HD broadcasts, so if you don't have HD presently then it shouldn't really matter.
However, a TV IMHO is one of those things, (like a PC), that it makes sense to buy the very best one you can afford too in order to try and 'future proof' it for as long as possible.
You may not have HD now, but you may decide to get it in the future.
FWIW when I bought my currently TV I was advised to get either Panasonic or Sony by an AV engineer. I went with a Panasonic Viera, and it's a cracking TV