External GPS or iPhone 5S maps for first time driver?

I just got my driver's license and getting acclimated to driving, and I need a GPS to assist me. Which would be the better choice to use for a GPS: an external GPS or my iPhone 5S's maps GPS feature? I have been using my iPhone the past couple days, but I'm curious if using a real GPS would have any advantages over my iPhone's maps application.

I was browsing GPSs on Amazon and the Garmin 50LM came up as the best choice (top-rated), but I'm definitely open to suggestions of there are others better. I'm not really on a budget, but I saw the Garmin 50LM is around $80, so I'm looking about that range.

Either choice, an external GPS or my iPhone, I would mount on the dashboard.

With iphoen 5S you just ask siri for directions to so - so… Then it speaks the directions as you drive