I would skip both boxes.. As tempting as their offers may seem.. It's always best to buy your own battle tested hardware and just install a compatible IPTV apk on it.. Or run it through Kodi's PVR & EPG addons.. You get much better performance and stability that way.

By battle tested, I meant devices that some of us in here own. Been using for long and or for various purposes. I did give some examples.

See, now you mentioned about your TV type. Unless you plan to upgrade the TV soon, pairing a Shield is definitely overkill for that TV and your needs. Cheapest I'd recommend would be the Mecool. Yup, do search for the service first. Some allow free trial and others do not cuz they are either very good or just want to run with money. Either way, know that any monies paid is considered    .. Ain't coming back. So try to sub for a month max.. test and if okay? then extend.. Else, just forget and pay for another service. rinse repeat until you find a suitable one.

MI Box S if and only if you want Netflix FHD. It's a certified box and can go up to UHD (if no issues).. But if not keen about Netflix and prefer a more functional or apps friendly box? Definitely go for the Mecool M8S Pro L or its successor the KM9. It's great to have a budget, but don't fixated too much on it. Cuz IMO, better to spend slightly more and get something that works now, all the time and is future proof. Than to buy a box just cuz it's cheapest, only to suffer AND later buy the more expensive one to get what you want done. Don't forget to set aside money to buy a separate keyboard + touch pad/airmouse combo. You'll need that for some apps that require touchscreen input. You are welcome.

The KM3 is better than the KM9... Don't let the numbers confuse.. 
Hmm.. Hard to tell at this point as I don't personally own the device. As such will have to rely on other owners feedback... Perhaps later, I'll skim around and report back.