I started using iPhone apps and then "graduated" to a Garmin Edge 500 with HRM, Cadence and RPM. One day out on a ride, the Garmin's battery dies. Turns out I enjoyed my ride without all the information (and the Edge 500 is customizable). So I sold it all on eBay and now I just rely on the iPhone. Can't speak to data issues, my employer covers that . I don't use any of the sensors since I found that info useless when I had the Garmin.

I wanted the Garmin badly only to realize that I really didn't. I don't think you're going to get the "right" answer because it will be a personal decision. Enjoy the journey.