Strava and ridewithgps are good and popular. I use ridewithgps and am very satisfied. I used the free version for over a year and then switched to the paid version. Many are satisfied with the free version. I suspect data usage is not much at all. I haven't tried to use it with the phone in airplane mode, and I think there's a good chance it will record the ride properly but just won't display the map, so if you don't need to look at where you are, you can run it without using any data.

The data and graphs these apps provide are excellent for fitness tracking. I wanted to improve my average speed and had a tough time for about a year. Then I read about high intensity interval training (HIIT), and I rarely do it properly, but every so often, I'll pedal hard for a minute at a time. This builds both strength and endurance. One thing that really helped me is the graph that shows how much time I spend at each speed. I was hanging out at 13 mph a lot of the time and rarely any time above that. I pushed myself to keep it over 13 mph, and now I'm much faster overall.

Last year I set a goal for hitting 2,000 in the calendar year, and I achieved that. This year's goal is 2,500 miles, and I'm almost on target for that.

These apps are also social media, so you can see other people's rides and routes and make comments on them.