Younger: Intelligence.
Now that I'm middle aged: Strength.
Honestly. The older I get, the more unhealthy I see my peers. My demographic spends their days in a cubical..getting unhealthy. Then, they struggle with shoveling snow, and have heart attacks by 50.
Shit. I can't believe I'm typing this. Me just a couple of years ago would say "Intelligence, hands down."
Don't get me wrong, I still read a lot, do sudoku before I fall asleep at night, and me and the missus do crosswords together. But, the older I get the more I feel proud that I'm (relatively) fit.
I'd rather be the guy with an IQ of 100 and live a ripe old age and play with my grandkids than be the guy with a 150 IQ and die raking leaves at 45 because I spend my days typing TPS Reports in a cubical.
Now, in a week, if I slip a disc in my back while wrestling with the high school team I coach, then I revert back to "Intelligence is the most important aspect for people".