Chromecast Ultra is the best buy if all you care about is streaming from your device and you don't care about a remote control.
If you are looking to save some money go with the older model Chromecast which doesn't support 4k.
If you want something a little better consider the MiBox or the SlingTV option.
The best AndroidTV option is the ShieldTV by far.
If all you want to do is stream Netflix to your HDTV and control it from your phone, get a $25 Chromecast.