I've seen both sets but not near each other. In fact, they were in different stores. But that doesn't matter since I find it impossible to judge fully a picture displayed in a store. I go mostly by the calibration reports of those that I am familiar with.
The F5500 that I saw was a 60 inch unit and the black level wasn't impressive. Yes, I did adjust the controls to where the Samsungs look best. The ST60 also was a 60 inch and its black level looked good even in a brick/mortar environment. The picture appeared nice but beyond that, I couldn't see anything more to comment about.
Cost isn't much of a factor. My current 64D7000 still looks good (except for a slightly annoying screen uniformity issue) so I'll probably wait a while until I can see the Panasonic 65ZT and 65VT models -- although I can't imagine that the ZT will be worth over $4000 delivered. (I have no interest in 3D or any of the 'smart' features. Beyond looking to see what they are like, I have never used any of that stuff on my D7000.)
I guess that I would have been a dissenting vote in the focus groups that convinced Samsung to make a model, the F8500, so bright that it can burn a hole in the wall opposite the display.
I've worked on enough D and E series models to know the calibration problems that occur when the contrast is reduced and, for that reason, I'm leaning toward the ST this year. Although, the VT... ??