I prefer maps for long rides out in the hills... If I'm just trying to get somewhere local quickly though, I use my phone. I was originally looking at the Garmin Edge with maps built in, but it's ridiculously expensive, so downloaded this app called Cyclehub. Designed as a Sat-Nav for bikes, and it's bl**dy brilliant... well - for free anyway.
Maps are better when you're out in the middle of nowhere, because you can see your current point and your destination and everything in between. That's simply not possible with a phone. Zooming out you lose detail. Zooming in you lose your start or end point.