Good wi-fi routers support multiple wi-fi bands (at least both 2.4GHz and 5GHz signals), have wireless-ac, great range, are reliable affordable. A really great wi-fi router makes sure there as as few 'dead zones' in your home / office as possible.
Router safety tip: Use WPA2-PSK (AES) encryption for the best speed and security on your Wi-Fi networks. On older devices use your router’s mixed-mode setting, AES and TKIP.
The best wi-fi router for normal use: TP-Link Archer C7 (v2) (great price, useful in larger apartments and multiroom houses)
The best affordable wi-fi router for normal use: TP-Link TL-WDR3600 (best for apartments and small houses)
The best wi-fi router for normal use with more features: Netgear R6400 ( easier-to-use UI, great price-to-performance ratio)
The best wi-fi router for Apple households: Apple AirPort Extreme (Apple product, so expensive)