(Opinion question)What is the best router for small business w/ VoIP setup?

I am having issues with our network & voip and the router we have is not that good.

In need of a router under $500 that can handle traffic of about 15-40 people intermittently as well as have good enough setting options to allow a detailed and good setup(i.e. QoS, Firewall, Ports/udp, etc) for a VoIP to handshake with its server over the internet.