I have both a Garmin GPS (at least my 4th Garmin) and Android phone with Google Maps. The only place the GPS has an advantage is when there is no cell signal (and Google Maps tries to prevent that problem by loading maps ahead). With Verizon cell service, I seldom encounter a situation where Google Maps can't navigate. With cell coverage ever improving and Google Maps constantly improving, it only gets better.
My main issue with the GPS is the user interface. I can find a destination almost instantly on the phone, with the GPS it is usually a frustrating experience. Google Maps quickly fills in what you are trying to find while the GPS keeps telling you it can't find that location, place, etc. I use the GPS mainly as my speedometer as my RV is off 3-4 miles/hr. If it weren't for that, I would not use it at all except in emergency cell gaps. And Google Maps recently added speed limits.
Google maps (since it knows all about what everyone is doing :) ) has saved me quite a few times from traffic accidents or just heavy congestion and it turns the route yellow and red to indicate congested areas. Just recently it routed me around an accident on an Interstate highway without me doing anything but giving permission to alter the route. I quit even connecting my Garmin cable for traffic data because it seldom helped.
Anyway, I certainly would not buy stock in a GPS company.