While Samsung Plasmas in general did get great reviews last year, I don't think it's right to assume that they'll be better than the LGs this year as well.
PK550 has got a fair number of reviews and they've all by and large been excellent (albeit PK750 hasn't got good reviews). Unfortunately, the reviews for the Samsung C550 are fewer (CNET, Cleveland Plasma) and I haven't yet seen one that suggests it's in any way better than the PK550 or (even as good as) last year's model B550.
Here's a link to Cleveland Plasma where Chad B's reviews for 2010 TVs (including C550, PK550 and G20) are posted. I'd suggest folks go through it before making decisions.
https://clevelandplasma.com/store/2010_television_reviews
I have nothing against Samsung. A lot of the gadgets/devices at my home are from Samsung and there's a good chance I'll buy a Samsung TV as well. I just think, we should treat each TV on its merits, be prepared for surprises and not judge based on past experiences. Things change very fast in the world of electronics.
In the end, no matter what TV you buy, I hope it serves you well.