Difficult question because each has its pros and cons.
If you have the VT50 in a medium to darker room, then you're gold. If you need a set for a bright room, then the F8500's brighter picture wins the day. The VT50 gets IR fairly easy but the F8500 is very resistant to IR. The VT50 can be calibrated to reference level without a LUTs processer. The F8500 requires a LUTs processer to be calibrated to reference levels but with that said, you can use the internal CMS to get a picture that is fairly high quality. Personally, I don't want to run the signal through any more processing than necessary and would rather not use the LUTs processer. The smart app for the VT50 using small jpegs for your picture files which is worlds better than not having them in the F8500. We use the smart apps to access photos off of the computer and its just a lot easier with the VT50. VT50 is heavier which would give you the impression that it should be built better but for some users, they get the yellow blobs. I don't have them but its always stuck in the back of my mind. Given the number of hours I poured on the VT50 for a year and a half (probably over 3 years normal use) it works like a champ.
One thing that can't be over emphasized about either display is if you really want the best picture and can see the difference in colors like gold versus raw sienna, then getting a high quality pro level calibration from a calibrator who has a jeti 1211 spectro or equivalent is a requirement....not an option. I got my three i1D3s profiled off of a jeti 1211 and the difference is visible.....but then again, I'm a bit extreme about PQ...and SQ(sound quality).
Samsung 64F8500, Panasonic 65VT50, Oppo 95, Tivo Roamio for OTA, Dish VIP722, Marantz AV8801 preamp, Rotel Amps, Atlantic Tech 8200 speakers, Seaton Submersive HP, Calman 5, Chromapure, Accupel DVG-5000, i1Display3pro, i1pro2, eecolor colorbox.