iPhone + Lifeproof.com case to get it IP68-rated + RAM mount (x-grip) and then the Tomtom GPS app. iPhone works pretty well since it's an LCD, not AMOLED, the AMOLED's that many Androids use really really suck in sunlight.
Bluetooth sound obviously works perfectly, and you can play music while riding in the background; if the GPS needs to issue instructions, it lowers the music volume automatically so you can hear it clearly. Been using it for years now in cars and on the bike and to date it has worked perfectly. Plus, no extra box to haul, just the phone which is nice and secure there, and when you get there the phone is fully charged (also have an outlet on the handlebars).
I'm sure the bike-specific GPS:es work very well, but they're priced outrageously and it's just an extra box to haul. The Tomtom GPS app is at least as good as a standalone GPS, and you always have it in your pocket.