What is the best Couch-to-5K program on the watch (total beginner)?

The easiest program is to follow Jeff Galloway run/walk approach. Pick a goal to complete 5k without a target time.

If you install the run/walk data field from the IQ store, the watch will also tell you when to walk and run during the workouts. If you are a total beginner start gently 1mn run/1.5mn walk. After a couple of weeks, take 15s off the walk time and add it to the run time until you get to 2mn run, 30s walk for paces in the 10+mn/mi.

Thanks for your reply! I have in the meantime already started the 5k program with Greg McMiller. I have now done my second "run" today after the benchmark run and am in 1st week. My knees, hips and legs hurt, but this is expected as a total beginner.

As you said, the watch told me exactly what to do and how long – this is so great, I never expected this. So the watch is now my coach and I won't need any plans printed out by computer any more!

Glad you got a program. Having no idea of your age (I'm an older guy), or your aerobic capacity, my take would be to start slow and go short. Don't get frustrated if it takes some time. Mix in a bunch of walking to get your body used to the movement. You can pick the up the walking pace as the body adjusts, mix in some jogging as feels right and up the distance as you progress. Not too far down the road (so to speak) the jogging will give way to some light paced running. If you press too hard before hardening up by getting your body ready (working into it), the chance of injury goes up.

If you have access to a gym, you could mix in some treadmill work. The impact and resulting soreness will be less. It's is a not a bad way to improve aerobic capacity and you can terminate the exercise any time. Lots of folks can't stand the "dreadmill" but I kind of like it, especially since I have a gym that lets me pack in my own fan (I don't do heat well).  It will take a while to see the weight benefit, at least that how it works for me. Initially, if I've laid off I'll get hungrier as I work back into shape, then the huger dies down. The conventional wisdom for walking or running is a person burns about 100 calories per mile. A mile doesn't do that much but as you build up, the calories start to add up. And when you get adjusted to the load, you body will begin to crave the exercise.

If you've been sedentary pay attention to how your body feels and watch your HR. No use getting a coronary trying to go from couch to fitness. Everybody's nominal exercise HR is different. I run higher than average as a norm and that's fine, I have decades of exercise behind me to tell me that's OK. You're just starting out so take some time to figure out what a comfortable HR is for you. Comfortable is just a catch phrase to say don't stress yourself too hard before you know you can handle the stress.

And there's a rub with the optical HR on the 265, I have to be in an exercise for about 10 minute before I place much faith in the reading.I have a post with graphs that show it. 

3 decades ago I took on a fitness challenge, sort of on a dare from a friend, I did the challenge (it was a week long cycling event that took a lot of prep for a guy who was just starting out). But I dug it and afterwards I expanded on it. He literally changed my life. That friend moved far away but I thank him often in my thoughts. Set a path that keeps you from getting discouraged, work into it and I think you will enjoy much the same.