Two fairly different frame geometries, why do these end up in the final two? I'd take some serious rides on each and figure out which fits best and will be most comfortable for you (as the other posters mention), and maybe even compare amongst similar frames once you choose between these two (i.e. the TCR composite is similar to specialized's Tarmac for one). I'd also lean away from the Trek for purely personal preferance for the less-commonplace, non-behemoth makes (that said Giant is nearly as ubiquitous)...no arguing both are great bikes and good values. I suppose I just made the case that this is a personal thing (amongst similarly capable bikes in a similar price range) and at the end of the day, you just need to buy whichever's most exciting to you.