So I bought a pretty good 800€ smart tv.
The problem is that that thing doesn't have a android tv, so it's pretty much shit and it's not accept very big mkv files (70GB)
I just want a tv box so I can hook up my 3tb hard drive basically.
Anyone recommends a good under 70€ box? Make sure it's compatible with 3TB hard drive.
All you need is video playback? If that's the case how about putting Kodi/LibreElec on a cheap NUC?
I have no idea how the cheap Android boxes do with 4k. One of them will probably suit your needs.
I was tempted for xiaomi mi but it doesn't have ethernet. I'm affraid it will lag if I try to play 4k videos on netflix.
Always buy a TV based on picture quality. Then attach a box to it that you can upgrade.
As far as your options, right now there's two devices running the Android TV operating system: $70 Mi Box and $180+ Shield TV. If you're not doing 4K, then just get a Mi Box. If you want top of the line performance and to run a Plex server, then spend the extra dough on a Shield TV.
For what you want to do the only real option is the Shield. Anything less and you'll be pulling your hair out in frustration frequently.
The is a whole LibreELEC community dedicated to running a highly optimised version of Kodi on cheap AMLogic S9xx Android boxes:
https://forum.libreelec.tv/board/38-amlogic/
Android will just get in the way if all you want to do is playback your own content from a direct connected HDD.
Those boxes running AMLogic LE Kodi easily handle high bitrate 4K because of the optimised Linux based operating system used. Most will even do correct colorspace switching from (rec.709) SDR to HDR (bt.2020) and also 1080p <<-->> 4K resolution switching.
Far superior to anything Android has to offer.
So I bought a pretty good 800€
smarttv.
FTFY
The Shield TV is the only good Android TV, but it is out of your budget. I would get that the Roku Ultra, which appears to be the only current Roku device with USB expansion. Still a bit over your budget, but much less than the Shield TV.