Have you tried Viewranger on a smartphone? Latest version is excellent and I love how you can buy individual map tiles (you buy maps credits in batches)

I wouldn't consider walking without a map. Phones are not reliable enough to depend on.

Both.
GPS as main navigation, map as backup. I keep the map open at the correct page in a transparent map folder rather than getting waterproof maps.
I would rather not have to use the mobile if possible owing to battery usage and quality of maps. The GPS units I have seen seem much more detailed in that regard, also waterproof
Will take a look at ViewRanger though.
Personally I go for phone and spent the money on a Spot Gen 3 as I hike alone and keeps mum happy.
http://www.findmespot.eu/en/
I have a garmin eTrex20. It does loads of stuff that I dont use - I just look at the map on it.
I plan a route on plotaroute.com then save it on the garmin and follow the line.
It comes with a very rough base map which is no good for any kind of navigation and it's expensive to buy OS maps for it but there are free maps (OpenStreetMaps/talktoaster) which are almost as good as the OS maps.
Never tried any phone apps. I dont think the phone battery would last long enough. I usually take some spare batteries (AA) for the etrex and can swap them if it runs out.
I also have a spot tracker (just to be clear - it doesnt do any sort of navigation) and it's a brilliant thing to have.