Go with what you like the best, which is usually, but not always the more expensive one. At the risk of muddying the waters, I would point out the Specialized Sirrus Sport which on paper looks to be as good or better a bike than the Trek 7.3, is currently on sale for $475. Also check out the Jamis Coda Sport and Coda Comp, both of which are steel frames rather than aluminum. All things being equal (and they are not always equal), I would take a quality steel frame over an aluminum frame for hybrid and road bikes.