Motion X GPS (non drive) works well and is cheap.
Navigon and other gps apps are good too but can drain the battery unless you have the right charger.
iPhones don't work well with gloves and are way too fragile. I had a 3S mounted for awhile using motion X and the glad broke when I took a spill. If you use the iPhone as gps you need a spare phone for emergencies.
But still, I'm having a hard time pulling the trigger on a $500 Montana because it seems like dealing with it's software issues is a full time job.
I just want google's MY MAPS and routes to show up on a bombproof iphone or Android. Routing in google is SO easy and by using terrain and Sat images, I can find the best roads.
For my weekend riding and trips to neighboring states, my written turn list has been all I need. It's not tech sexy but it works and I spend more time riding and not watching a gps.
If I was planning a longer trip I'd have multiple GPS units
and an iPhone.