There's much discussion on all sorts of technology sites around whether standalone automotive GPSR's can compete with smartphones.
For someone who already has a smartphone, the answer might be stacked against the dedicated GPSR depending upon precise end user needs, but for someone who doesn't own a smartphone there's still a clear cost advantage to the dedicated GPSR - at the moment anyway.
What's interesting is to consider the evolution of automotive GPSR's over their relatively short lifetime. Garmin devices tended to be quite expensive "enthusiast" devices with a great, rich, feature set but sometimes arcane user interface. Then Tom Tom came along with cheaper, but far less functional devices with a great user interface. Tom Tom hasn't really deviated from that model ever since, but Garmin's response has been to ape (and perhaps overtake) Tom Tom's simple intuitive user interface while "dumbing down" the functionality on offer. This "dumbing down" means that the fairly rudimentary functionality that a smartphone-base solution offers is now super competitive, if you already own a smartphone.
If you want or need some of the higher functionality features, such as complex off-device route planning, multi-stop least cost routing, etc. or you need a waterproof unit to use on a motorcycle, then a dedicated Garmin device is probably still the best bet. However, if your navigation needs are along the lines of "get me to an address by the quickest / shortest route", then there's probably little to choose between Tom Tom, Garmin and a smartphone-based solution, assuming you already have a smartphone.