Nvidia shield if you want the absolute best box on the market....then take your pick after that as all are mostly the same apart from the odd feature here and there. You have the mi box s, I have just recently purchased a Vodafone TV box ($72 aus dollars with a RF antenna built in) essentially a mi box, technicolour, blaupunkt all make box's.
It depends on your budget and your use.
price < $100 mibox
$100 <price NVIDIA Shield Android TV
Nvidia Shield