I never tried that one, but an IoS one that I did use was NavFree.
What I liked about it is that you could download maps over wifi before your journey so I could use it on the ipad without any need for data.
You have to pay extras though if you wanted things like speed cams or foreign maps and fancy voices.
I dont have my ipad any more and its a while since I used it, but the version I had only had 1 voice - which was good enough to get me to a friends house after she'd moved to the middle of nowhere and I didnt have a clue where I was going. I took the ipad because of the larger screen, but I've no doubt they will also do an iphone version.