i haven't seen the lg in action, it gets excellent reviews though. i've seen the vt20, and it's a brilliant tv imo, with very deep blacks and a sensational hd picture, sd is also excellent. but, this years pana plasmas (at least the v series) do suffer from some minor niggling problems.
some have what's described as "floating blacks", this is a slight rise in black levels during some scenes, i didn't notice any on either of the v20's that i had (they are identical to the vt20 bar the 3d functionality, i returned both of mine)), but many people have seen this, how much of an annoyance it would be, or how widespread it is i'm not sure.
the main issue with the vt20 though is it's inability to deal with motion as it should with 50hz sources, dvd's, all tv, sd, hd. but not blu-rays. this is something that apparently affects all v series sets, although it's not a major issue imo it was enough to put me off the v20's that i had. however i paid the full price back in august, if it had been much cheaper i might have lived with it
how it manifests itself is slight judder, blurring when there is a panning shot, like you see in the programme "dragons den" as the camera moves from one dragon to the next it is evident, turning on the IFC, which is panasonics motion processing, does solve the problem, but introduces artifacts and gives a false, robotic look to motion, it's poor to be honest and i always left it turned off. i didn't see this problem with blu-rays though, they played back flawlessly with IFC turned off..
it seems that some people are more succeptable to this than others though, as a friend of mine couldn't see the issues on my tv's even when i pointed them out, and there are many vt20 owners that are very happy with their sets.
i'd be very tempted by the vt20 at £1299, the best thing is to demo both tv's though, see which one you prefer, to my knowledge the lg has no problems, and if you do plump for the vt20, i'd get a guarantee of a no quibble refund in the event you find any of it's quirks too annoying, if not, it's a fantastic tv..
ps.. having said all that
, if you could wait a few months then better 3dtv's will be available, but they will cost more..