If the Oppo UDP-203 is still in stock, GET IT. That is seriously one of the finest pieces of gear for 4k UHD. It's awesome. If you have the ca$h and think an all-in-one video AND audio device is in the playing cards, get the UDP-205 if it's still available.
The UDP-203 should be $550-$600. However, they are price gouging on websites like a crazy Florida homeless man on crystal. The UDP-205 should be around $1200.
However, Oppo has stopped production, so let's pretend it doesn't exist now.
If you want Dolby Vision (and that's a good idea), I would suggest the following, in order of price (low to high):
Sony UBP-X700
Sony UBP-X800 (don't quote me on this, but I THINK they are going to have a new version of this model soon)
Panasonic UB820
Panasonic UB9000
It's possible that the Panasonic models are gone now? Sorry, I am heading out the door so I haven't checked this in a while haha. Maybe I will edit and update more when I have the time.
Also, coming soon to the U.S. will be the Pioneer Elite BDP-LX500... a killer flagship 4k player.
Dolby Vision will most likely be easier to find in players next year. Hopefully.