I have Navigon but prefer Maps interface
I hate the interface of Navigon. The exit button is buried in nested menu. If you changed your mind after navigation started and don't exit Navigon properly (hard to do while you are driving. Hitting the home botton or switching to another app will leave Navigon running in the background) it will continue and drain your battery really fast.
Entering search information into it is a pain. You have to enter each field in reversed order: state, city, street, number. Search for a POI is a pain: you have to select a category for the POI first. Often I give up and use the Google search option within it. It's not intuitive to use an address in your address book either.
Apple's Maps is a breath of fresh air with Siri integration. I got in the car on Saturday morning with 15 minutes to drive to a restaurant to for a birthday brunch that was about 20 minutes away. I asked Siri for directions to restaurant_name and in a few seconds I got turn by turn directions. I have uses Maps for only a few times so far but it worked flawlessly for me every time. I love the clean look of it.
Sure, I find Navigon lane assist useful at times, but I can get by by reading the signs myself. I think Apple's Maps is a really nice product and for where I live it is accurate so far. And I am sure it will get better.