Plasma over LCD every time.
No motion blur, better off-axis viewing, better black levels, no input lag, so on and so forth.
That may be a fine TV, but unless you can't live without 3D or your room is VERY bright, I'd go for a Panasonic V-series plasma. If you can find one, the 50" should be right around that price range. If not, a G-series would save you a bit of coin and offer excellent performance as well.