The exercise that integrates best with muscle growth is undoubtedly walking. It's insanely easy to do and distributes the workload throughout your entire body. Currently my total daily steps range between 10 - 20,000 steps. As you can see, I average 15,000 steps a day.
As long as I get that, all the cardio I need is getting done. As long as I control my diet and lift 3 days a week, it's awesome. I can walk for hours -- and I do! Remember, you don't have to be huffing and puffing to get a cardio workout. On the other hand, just because your body is burning fat for energy when you walk, this doesn't mean you're going to get leaner if you're in a calorie surplus.
In the final analysis, walking is a great stress reliever, helps digestion after a meal, helps you sleep better, and means you're probably getting more vitamin D from the sun. It helps you burn unwanted body fat and prevents it from being stored in the first place. Walking is amazing and we should all be doing more of it. It's the best way to get lean.
Thanks for attending my TED talk.