My company has it's own internal running club and apparently uses Strava to log participation and I figured I'd check here to see if anyone's using/tried it...
I found it to be the best one for phones. I use it when my Garmin isn't working right or if I don't have my Garmin on me. I also use it to back up my Garmin data online.
I tried Strava and Endomondo on my phone. I eventually decided on Endomondo but I can't really remember now why I chose it over Strava, so I guess I can't be of much help other than to offer up Endo as an alternate choice.
I'm on Strava - a few friends that are scattered around the world use it and it is nice to keep up with what they are doing. I'm also in a work-based group. I use an old motoactv running watch and upload activities manually as tcx files - it's not too hard. If you've got a phone or something more modern like a garmin watch you should find it a bit easier to keep up to date.
I copped a pretty bad injury a few months ago, and having a few years worth of historical data comes in handy.