First and Foremost, decide what your Fitness Goals are.
Then, you need to choose from among various Fitness Protocols, which one would best suit you, to attain your Specific Goals.
You can do this yourself, if you know what you are doing. If not, talk to a Qualified Professional, and draw up a Training Plan that will help you achieve your Fitness/Health Goals.
Once you are comfortable with your Training Plan, stick with it. You will need to review and update this periodically.
Have said this, here are some pointers:
1. Strength is the MOST basic of ALL fitness and health.
2. Strength is the MOST useful in general, in life.
3. Strength once gained, never leaves you.
4. Strength Training will improve your Cardio quite a bit (although for specialized things like to be able to run a Marathon, you will need Specialized Training)
5. Strength Training Builds Strength, Builds Muscle and Improves Bone Density
6. Cardio is easy to gain and can be gained fairly quickly….
7. Cardio is easy to lose and can be lost fairly quickly…
8. Doing too much Cardio, makes you lose muscle
9. Cardio does NOT build Strength, except a little, for a very brief while
Add to this, the fact that we ALL (all humans) tend to lose Muscle Mass and Bone Density over the age 30. This loss accelerates more and more as we age into our 40s, 50s and beyond.
These are some of the things to ponder, as you make your decision.
Hope this helps!