Don't crazy downvote me here, but is there a particular reason you're not considering the SHIELD?
I retired my nexus player. I dont have any experience with Mii box, but I can tell you that going to a nexus player will frustrate you with its choppiness and lag.
I'd love you guys imput :) Heres what I was asking
Hey guys I want to get a android tv streaming box for our upstairs bedroom. We have a shield tv downstairs that runs my plex media server so I don't need another shield just to stream netflix and sling tv and channel apps. What does everyone think is the better buy the mi box or the nexus player? I know the nexus player is older(did it come out in 2014?) but it is getting android 8.0 and the mi box is still on 6.0.1 so there's value in getting updates there. Even if the nexus player never gets another update its still worlds ahead of the mi box.
As someone who owns two NP's they are really long in the tooth. I would probably go with the MI. That being said, and as someone who is a total Android fan boy, id actually recommend a Roku.
A year late..
I have both, MiBox gets more use though. MiBox is certainly faster than the NP, however the NP is getting more updates. I heard a lot of people had issues with Netflix on the MiBox, I used to but found a fix for it that has worked for me. Overall I liked the MB more, it has a better remote (volume control) but I ended up using my normal TV remote which has CEC functionality which allows me to control my ATV without the native remote.
Nexus player is good if:
You don't go anywhere near 1080p / 4K HEVC video compressed content and enjoy a slow hardware dated device with only 1GB RAM - this is the killer 1GB RAM.
2GB RAM is the minimum these days if you want a decent Android TV device.
Forget about 10bit HEVC video playback or VP9 - now used by Youtube. The old Nexus Hardware does not support these.
BTW: The Shield does not support VP9 profile 2 - that is being tested by Youtube either.
Even the Beta Nougat Firmware floating around for the Mi Box is fine.
I own two Nexus Players and one MiBox and the Nexus Players appear to be more stable than the MiBox. MiBox has a few nice things, it being slightly faster, remote has volume buttons, full USB port in the back, but the Nexus is more stable, has fewer bugs.
Is a Shield within your budget? Because it's the best you can get right now.
Otherwise, it might be better to go Nexus if you don't want 4k. I've been hearing about a lot of issues with the MiBox.
I have 2 MiBoxes that are really solid. I know they are reportedly hit or miss, but I have 0 issues with mine and recommend them all the time.