"Beat Yourself" or "Beat a Friend" real-time audio coaching
This is one of, if not the most, effective training feature that I use, and value immensely. It has shaved considerable time off of my efforts.
I'll start off by saying that I love Strava. That said, I am still running two training apps side-by-side when I train (only because Strava doesn't currently have the "beat yourself" feature). For this feature, I run Endomondo at the same time as Strava. There is no question that Strava does everything else better.
The functionality that I would love to see Strava add is the ability to race agains yourself in real time (I would be happy if they just added the same "Beat Yourself" and "Beat a Friend" functionality from Endomondo, but I have no doubt that Strava would probably even make this feature better).
THE "BEAT YOURSELF" FEATURE allows you to select a segment that you or someone else has already run/biked, and race against that effort. You can select the parameters around how you receive real-time audio feedback. For example, you can receive feedback every xx miles, or every xx minutes. The audio feedback will tell you (in-real time) how your current effort is stacking up against the prior effort that you selected for that segment. For example, I often run a time-trial route up a local mountain. I will select my PR on this segment to race against, then I'm off. The audio coach will tell me every 2 minutes, how I am doing relative to my PR - e.g., "You are 10 seconds ahead of your PR." Talk about motivation! You can also set the audio coach to tell you other helpful statistics such as lap pace, speed, elevation gain, etc...
This type of feature has been the best training feature that I've used and I would be very grateful if Strava would add this incredibly valuable feature.
Justin F. (Boulder Colorado)