Looks like there's a good amount of them out there:

Top 10 Bike Navigation iOS Apps

Wondering which one is the best?

I tend to use google maps app. Not perfect since it tries to use every cycle path and sometimes goes on streets that aren't exactly bike friendly, but does turn by turn with street names so I can leave the phone in my pocket. I think its interesting they didn't include it.

What I have done is use "mapmyhike" and I can compare routes I've all ready ridden to see the best option...

Google & Apple maps accuracy & showing best path does not always fit reality. For example I looked up (for someone else) cycling directions from Doyle elementary in doylestown, to the septa station. This wasn't really for directions but for a time estimate, and both google & apple maps gave me weird and longer routes. It's a straight shot down west st, and it took me thru center of the borough.

I tend to use google street view to double check routes that apple maps gives me, and mapmyhike to then compare once I've done the trip.

I'll have to look into some of these other apps & see if they are worthwhile...

- Andy