The lack of hardware support for a few modern codecs is a pretty big complaint from me, but nothing else out there is decent :/
The Apple TV's pretty good. I imagine I'd have a hard time switching to a Shield TV unless it gets a CPU bump, whereas Apple still keeps making newer models with modern-ish phone SoCs.
It depends what you're looking for. In the AV enthusiast circles a lot of people flock towards the Ugoos AM6B Plus (with CoreELEC).
It is one of the only devices (alongside Oppo clones) that can play Dolby Vision Profile 7 FEL (Full Enhancement Layer) with 100% accuracy. The Shield can play P7, but it ignores the FEL data; the Ugoos actually processes it.
That said, people don’t generally use Android on it, instead you boot to CoreELEC from an SD card and use Kodi.