The main difference is that the Pro uses Lightbridge and the 4K uses Wi-Fi. That means you'll be able to fly further or at least run into less issues connection-wise. If you're always going to be flying in wide open locations, then Wi-Fi might work out just fine for you. Also, it's easier to find parts for the Pro since it's more commonly purchased.
If you have the money go for the pro definitely, but the 4k is also a very good drone, I have the Standard, paid 500$ here in Canada and I love it, camera is only 2.7 K but this is more than enough for me, I usually shoot in 1080 and it makes awesome videos.