Open addresses in google maps instead of apple maps
Unfortunately, you can't (unless you jailbreak your iPhone).
Anyway, from iOS 8, you are allowed to use your preferred navigator, once Maps has been opened:


Open an address (it will open with Apple Maps by default).
Tap the "car" button, as you do to get directions.
Tap the "share" button, then tap "Transport apps".
Choose the app navigator you prefer, among the installed ones (i.e., Google Maps). You will be redirected to the one you chose.


It's not as changing the default, but it's surely easier than typing an address manually in your preferred app.