I have nothing to back this up, but I'm going to say "eat healthy".

For losing weight, you really have to combine the two - how much you eat depends how much you exercise and vice versa.

But for general health, I think you can be relatively healthy without any exercise, but I don't see how you can be healthy for long eating only junk food.

Also, exercise takes time, eating healthy is not very time-consuming or expensive after you spend some time to learn some healthy recipes (if you have a kitchen and a refrigerator).

For Jelena and others wanting to do both: that's great, and possible! But if you're doing neither right now, don't start both at the same time.

Never start new habits at the same time unless they're really really easy. Take at least one months to make a behaviour a habit. Then if it's going well, add another. For something big like this, take longer!

Don't worry about how long it'll take. You can start around 8 new habits a year this way. That's not slow at all!

In my opinion doing exercieses is more important than eating healthy, but generally both things are very important. I think that attitude to life, family, true friends, successes in job are also very important to stay healthy. If somebody is alone it is hard to be happy then and when somebody is sad it can leads to health problems.

I try to do both but I'm not successful at it. Anyways, I think eating healthy food is more important, who knows maybe in that case we wouldn't even need to exercise. 

I think both eating healthy and doing exercises are important, but if we had to choose just one, maybe that's eating healthy.