Unless you can plug it in all the time I'd lean toward a real GPS, today's smartphone generally have horrible battery life with their huge colorful displays.
That's a good thought. My usage is mostly for day hikes and I do have backup battery and a solar charger so not normally a big concern. Plus I can turn off the phone features and still have GPS functionality.
But you're right, on a multi-day trip I would want a standalone with replaceable batteries.