FireTV 4K. Way cheaper than a Shield and is designed for TV.

Formuler z8 or Dreamlink T3

BTW if you don't already know, you won't be getting 4K through IPTV.

You can barely even get limited events from legit providers

Nvidia shield

I find STB Emu to be the most robust, if not best looking app

Ferguson ATVbox.

There are some great boxes from Dune,Ugoos,Minix,Zidoo,Egreat.

MiBox S