In principle the two system worlds are quite similar, so not much on either side to push the other out, but - to my current knowledge:
- advantage iPhone & apps: for most users easier to use and more intuitive on the GUI, a bit more serious appearing apps with quite some choices to pick from, more advanced A- of the A-GPS functionality even though the same GPS chip technology
- advantage Android: you are able to switch off mobile networking while using GPS, which I believe is the biggest issue with iPhones and the reason why I prefer iPad, where you are able to switch off BT and WLAN to get it mobile networking quiet
I do carry iPhone backup with navigation apps, but due to the mobile network issue would never treat an iPhone an all-day navigational aid (and some apps are not available for iPhone, but only for iPad, i.e. Jeppesen Mobile VFR & Jepp FD). With the latest smartphone generation battery drain also is not really an issue, your bladder lasts less.