Honestly you're going to have to decide that subjectively. They have the same "top gear" so you'll spin out at the same speed on both bikes. It just comes down to whether one fits you better or if you just feel more efficient on one vs. the other. Only two "major" differences I can see:

Trek has tighter gearing (11-32) than the Giant, which has a granny 34t chain ring so wider spacing between gears.
Trek is $100 more.