I'm not an expert but recently went through similar.
Seems the E8000 is not worth the extra over the E7000 (just the weird gesture/talk control features no one ever uses).
Panny v. Samsung - I trust panasonic more than samsung. But got a samsung in the end.
One thing to take note of the reviews for the ST50 etc. is they are nearly a year old at this point. They tend to 'win' based on value. As in, what you get for the money. The e7000 was several hundred dollars more at the time of review. You can currently get e7000 models for the same, or even less than the ST50 - as long as you don't want a 55" since Panny owns that size.
So for me, getting a Samsung, with damn near equal blacks (but no, not as good) and reportedly better PQ otherwise (colors, judder etc) dual processors vs. the single in the ST50 just made more since. Plus, it seems like Samsung has more 'deals' if you're patient and wait you can get a free sound bar, blue ray paler, glasses etc.
When I bought my Samsung E7000 it was $997, no tax, free BRD player and a total of 8 pairs of glasses. For $100 I could have gotten the ST50, no BRD player, no glasses at all. I would have had slightly better blacks but that's only one tick in my pros/cons list.
I guess what I'm getting at is don't just base your purchase on what one review says based on bang for the buck when what you get for your buck has changed dramatically since the TVs being reviewed were brand new models.
I wish it would have been a GT50 for that same $997 but they were asking $1399 or $1499 at the time. The difference in blacks and the THX cert didn't justify a 50% increase. At least not for me.