There are many great turn-by-turn apps out there, but the one provided by Apple's Maps is the one I use most often. The primary reason is how well integrated into the whole OS it is. All I have to do to get home from anywhere is just tell Siri to "take me home" and she takes me there. If that isn't enough to convince you to use Apple Maps for directions, there are quite a few other things you can do with Siri while navigating that make it totally worth it.
Once you've started a trip with Apple Maps, you may be traveling in an area with which you're not too familiar. If you'd like to know when your next turn or exit is coming up, simply ask Siri "when is my next turn?" and she'll tell you in terms of distance. If you'd like to know what your next move will actually be, just ask "what is my next turn" and she'll tell you the street name or exit number.
Are we there yet?
And of course, Siri can answer the age-old question, "are we there yet?" Simply ask her and she'll tell you how long until you arrive at your destination. The question can also be stated "when will I arrive," etc, but the former way is arguably more fun.
If you have any other Siri navigation tips, let us know in the comments!