Well I'm perfectly fine with my 4 series which I've had for the past three years. I guess the only driving issue is how important Dolby Vision is to cough up another 200 bucks. Otherwise its a push as none of em have true 120hz displays.
They're pretty good for budget/entry level models. Low end models like the S-series don't have Dolby Vision and they use a ClearMotionIndex to simulate 120hz. Also the Roku scanbar glitch manifests itself if you have the brightness set too high.