I'm using various apps on an iPhone 4s that doesn't even have a data plan. I have an old flip phone for emergencies. Cyclemeter works fine for recording my rides to review later. The only thing it won't do while I'm riding is show me a map of my current location, but it will show my time, distance, etc. After I get home (or to any wifi hotspot) the app updates to include the map. It does what I want from a GPS app -- just records my routes to review later. Handy to repeat a good route, or avoid a route or turns that didn't work out well. It's remarkably accurate, rarely more than a few yards/meters off from my actual position at any time during a ride.

I tried Strava, MapMyRide and a couple others once or twice. Didn't care for 'em, but I'm not interested in realtime feedback for riding speed, competition, etc.

I might be able to use realtime turn-by-turn directions but I'll probably need a data plan for that. I haven't found anything that works just off GPS for turn-by-turn directions.