I agree with everything Jaywalk3r said. A good example and a bike I've test ridden is the Raleigh Cadent i8

http://www.raleighusa.com/bikes/fitness/cadent-i8-13/

It's in the same price range as the Giant you are looking at and has internal gears, all the mounts for racks and fenders, decent commuting tires and is pretty light weight aluminum frame. But as he also mentioned don't get caught up on weight. If you are 170 lbs, you are going to account for most of the bike's weight so 20 lbs vs 25 lbs isn't going to make much of a difference. My new Surly is relatively light for a geared steel bike but once I added a rack and trunk bag and panniers and my locks and other stuff I carry regularly it gets pretty heavy. And if you go pick up groceries or carry a laptop or change of clothes it will get heavier.

Personally, I found that I really appreciate a steel frame for city riding because it soaks up bumps, pot holes and road vibration more then aluminum even if it's a little heavier. Another bike I test rode that I really like that has a crmo steel frame is KHS Urban X

http://khsbicycles.com/bikes/2013-khs-models/urban-x/

KHS has a lot of steel framed "urban" hybrid type bikes to choose from. But of course you might be limited to what your particular LBS carries. I'm still pretty new to being a "serious" cyclist but I have done lots of research, test ridden many bikes and visited several shops and I would prefer to buy a bike from a shop that I like with knowledgeable staff that I trust more so then buying from a shop because they carry a certain brand. And speaking from my experience I should have listened to myself. I bought my last bike from REI because they had it on sale for nearly $300 less then my LBS could get it for me. But my overall experience has not been great dealing with REI and while I saved money up front I can already tell you that within the next year I probably will spend that $300 taking to my LBS and having them upgrade stuff and set it up better for my taste