There's no such thing as a 1080i plasma. Manufacterers misleadingly advertise flat panels as 1080i when they are actually 720p. The 1080i is the highest resolution signal the TV will accept. All flat panels are progressive by nature.
If you want plasma get a Panasonic. Better PQ than either of those and far more reliable.
I have that TV. It's a great TV. Previous Panny plasmas had some problems that have mostly been eliminated in the 80 series.
The new plasma models will be out in a couple of months or so. You can probably get a good deal on the 2008s about now or within the next month or so. The only drawback with that is flat panel TVs are still relatively new and each new model brings significant improvments over the previous models. They cost considerably more for the first 4-6 months though than what you can get a last year's model for right before the new ones come out.
That said, I'm perfectly happy with my 80u.
If you read some reviews on the Hitachi plasmas they aren't very reliable and don't have the PQ of the Panasonics. Samsung reliability has never been anywhere near as good as Panasonic. I have seen people that prefer the Samsung PQ over Panasonic but not very many. I've seen the two side-by-side, the Panny is far better.
Don't believe anything Samsung says when it comes to contrast ratios. They have always way over inflated their ratios to make their TVs seem better than the competition.
Contrast ratio is the difference between the whitest whites and the blackest blacks. There are no standards for determining contrast ratios which pretty much leaves manufacterers free to claim whatever they want.
Even Samsung owners admit Panasonic has better blacks. That wouldn't be true if their contrast ratios were what they claim them to be.