I recently upgraded my tv from a 55" to a 75" and now all the low resolution content (720p,1080p) looks really bad especially YouTube. I watch a lot of YouTube content and most are not 4k.
A friend recommended to go for an Nvidia shield tv pro. I already have a fire tv 4k. Not sure if the Nvidia shield would do any good in upscaling YouTube videos.
Fire TV has the worst UI out of all the devices. Unless you're poor you will regret buying it.
Fetch TV ui is worse tho. But the real problem with Fetch TV is the amount of power it consumes while on standby. However Fetch TV DVR is a good alternative to streaming services. Pro Tip: You can replay fetch tv recordings on Apple TV using the VLC app as it's hosted as a DLNA server.
You don’t need the Shield TV Pro for up scaling, just go for the Shield TV. I don’t think the Fire TV will play YouTube any different to the built in app on your TV
Vero 4K is my go to
Even the highest end TVs will make that type of content look average. Only Sony can make it look decent. Shield does a pretty good job of upscaling but occasionally over sharpens and you can see artifacts around objects. But that is the only thing that will help really. Try adjusting MPEG noise reduction, and other noise settings on TV and see if it makes any difference first
Nvidia shield pro has fantastic upscaling. Best in class