Get the wired Roku. I have three models in a box somewhere and the wired one was far superior. Strangely enough my Roku+ would not talk to my ASUS router on 5GHz band despite both being close to the ceiling about 10' apart. The WiFi units will downshift the resolution without warning if any lack of bandwidth capability is detected.
After moving to an apartment I have two Sony TVs that have all the apps built into them and don't use any Roku devices now. I have no way of getting wiring to the TV sets from the fibre optics router so I am forced to use WiFi. 1K or 2K bandwidth on the 55" bedroom TV is not too bad but on the main 75" TV the 4K is nice. At the higher bandwidths it can be hard to tell what you end up getting but I think it is the sound that mainly suffers, missing the Atmos signals and flatter sound. 4K is no problem if I would move my PVR (DVR) back under the TV set and let the PVR cache the signals instead of the TV.