You want to stay fit and you dont have a lot of time.
your answer is power lifting. About three hrs a week.
what exercises? Bench press, dead lift and squat.
These three exercises use ALL of your body.
I can't do the explanation justice in this short answer, please read this article from Tim Ferris-
Google: "Pavel: 80/20 Powerlifting and How to Add 110+ Pounds to Your Lifts"