If one waits, one should wait for the Sony or the Oppo, which will have Dolby Vision, but will come in the summer (when the DV chipsets become available) at the earliest, more likely Q3 or Q4 2016.
The Panasonic is pointless (to me). It costs twice the price of the Samsung, but without Dolby Vision. Unless you believe in analog out for immersive sound (impossible, so completely pointless) or in the magical chroma upscaling (sure, that will make a huge difference), or in the value of a THX badge (when did it last make a difference?), I don't see the point.
IMHO, the choice is either to get the Samsung now to get in early and pay the price of being an early adopter, use it as a temporary player until a fully compliant one (i.e. NOT the Panasonic) becomes available later this year, or wait for a proper player, which will cost the same price as the Panasonic (Oppo) or likely less (Sony) if what you want is something you can keep a few years.
Most UHD Blurays will have Dolby Vision. When your display supports Dolby Vision (hopefully the JVC and Sony projectors next year), you will want to have Dolby Vision, if only because it's possible to calibrate accurately with DV, unlike HDR10.
Just my .2c of course
I'll be buying the Samsung as soon as it lands in the UK, and I plan to sell it for the first decent fully compliant UHD Bluray player, i.e. with
Dolby Vision, unless Cyberlink has delivered the goods by then and I can use my HTPC to play UHD Blurays with PowerDVD (it will likely take more time for non licensed options to become a reality, if ever).