My wife looked at both these bike this Spring. She ended up being more comfortable on the Giant and that is probably what should be your driver. I personally like the Giant frame a little better. The welds were much cleaner.
They are both very light, fast bikes. But we went for the Giant. We ended up trading in the tires (kendas 32c) for some Continental slicks at 28C. This is probably a good upgrade. Other than that, we haven't put fenders on yet, but with V brakes, that should work. Got a sturdy Trek rear rack and ended up spending a little over $600 US.
If you can, I would advise scrapping the tires and upgrading to something more flat-proof.
If you are worried about the quality of the Giant, I would remind you that they are both quality bikes and you should get a long time out of either of them. I think we've put on may 1000 miles on it this summer and everything is OK. I haven't even needed to true the wheels!