I've been using using most of the running apps and I like Endomondo the best.
Strava - It may be OK for cycling (I haven't tried it), but for running, I could never get it to display the distance/pace accurately on the watch (it displayed .12 miles when I'd run several miles). When I finished a run, the stats on the iPhone and my account at Strava were all correct. But if the watch won't display anything, whats the point. Seemed buggy.
MapMyRun - it only show one stat per screen on the watch: duration, distance, calories. to see this during a run, you need to swipe from screen to screen. Needs work,
RunKeeper - I've only used it a couple of times, so I can't really say a lot about it good or bad. However, I had some issues with the GPS staying on after I completed a run, and I don't like having to remember to go the iPhone to check to see if it is still running.
Runtastic. Its a really good app. The watch app shows duration, distance and pace on a single screen. if you swipe left, you get music controls. like most of the watch apps, you can configure which split announcements you want to hear if you are wearing headphones. My only problems are that the pace appears to be your average pace for the entire run, and not your current pace (if anyone knows how to change this, let me know). The other problem is that after I complete a run on the watch, the app on the iPhone doesn't always shut down the GPS - I've had my phone battery drain very rapidly because I didn't notice it was still on.
Endomondo - Its also a great app. You can configure two screens with three different stats per screen. stats include: duration, calories, heart rate (with strap), pace, distance, average pace, hydration and ahead/behind. You can also configure the announcements at each split. The pace (current pace) doesn't seem to accurate, but for me its better than average pace. So far I have not had any issues with the GPS on the iPhone - it comes on when I start a run on the watch, and shuts off when I finish a run on the watch (I haven't had to go to the iPhone to turn off the GPS, or shut down the app). for now, Endomondo is my daily app.
FYI - i only tried the Apple Watch workout app once... when i realized it was just a pedometer that used the GPS on the iPhone to "learn", I decided to pass.