Having used both, I personally prefer Strava. I've found it far better at motivating me to run. You can compare your performance against other runners along pre-defined segments (e.g. some hill you regularly run). The two people I've recommended Strava to are now hooked.

Their engineers make cool side projects [1] and release interesting new features regularly.

[1] http://labs.strava.com/heatmap/

Found a way to pull my runs out of Nike Running and export to Strava, Runkeeper or MapMyRun:

https://mattstuehler.com/lab/NikePlus/selectMyRuns/

Download your files, unzip, then upload the GPX files directly to the app of your choice.

Enjoy :)

Strava and RunKeeper are both amazing apps. I'd suggest to try them both and see which you prefer. It's a great time to be a runner!

Can you consider integrating Nike running into gyroscope? I believe they recently introduced new API for that, and I already have hundreds of km logged in