price.
It's kind of a hard choice. Both are good "cars" with similar miles and cost.
One is a sub-compact. The other is the typical mid-size FWD sedan.
For me, I'd take the Sonata every day, because it's bigger and built to a higher price-point and competition point. The smaller size of the cruz really buys me nothing (we aren't talking 3-series handling here) nor is the MPG advantage of the lesser weight enough for me to sacrifice leg-room for myself and the rear passengers.
Now if we were comparing the Malibu to the Sonata, it'd be a much more interesting argument. Or even the Cruz to the Elantra.
But for this comparo? I go with the bigger car.