If it's the VT20, it originally retailed for more than twice the price you mention. If you're choosing strictly between these two models, I'd opt for the VT20.
It's not perfect (scour these forums and others for threads about 50Hz processing and floating blacks), but it uses Panasonic's faster phosper technology, which the G20 doesn't. It can produce deeper blacks than the G20, as well, though there's not much in it.
In principle, the G20 represented the sweet spot in Panasonic's 2010 range, but given the relatively small difference in price now, I'd say it's worth spending the extra.
Oh, and unlike the G20, the VT20 is of course 3D-ready, as I'm sure you know. This may be of little importance to you, but the faster refresh rate of the VT20, designed to help with 3D performance, benefits 2D performance as well.