The Giant got good reviews in Bicycling Magazine. Their staff voted it the number one entry level road bike of this year. One notable comment is that they said it is upgrade worthy as you grow as a ride. I have an '05 Trek 1000, and it's a good bike for the price. They refitted it with a good mix of Tiagra components which I know is only a step up from Sora, but it is a good step. They also upgraded the fork from Aluminum to Carbon. The one thing I would do is upgrade the tires if you're on any road that has the potential to have glass or sharp rocks on it. The Bontranger Selects that come on the bike just don't feel that strong. I would get a more puncture proof tire. I got a puncture in my first week of owning the bike. I do believe that the component groups you are looking at on each bike are about the same. I don't know much about Bianchi so I can't comment on that. Other than that, go with what you find the most comfortable. If you can't make a decision because they all feel the same, then start looking at waranties, ask about parts, best value, etc. If you still can't make up your mind because everything's the same, buy the one that you like the look of the most.
I bought a Trek 1000 back in 90-91 when the fork was steel and not aluminum (back then the Trek 1100/1200 had the aluminum fork.) It was a good bike and served me well. I didn't cycle for about 6-7 years then this spring I started to ride again. It was back on the road after some cleaning and oiling. Unfotunatly due to some physical problems I had to limit my riding. I then switched to a recumbent. I now am back to some commuting and have joined a local cycling club, but I digress. I have no bad feelings about buying the Trek. Just that the dealer was horrible. No after sale support at all. Couldn't even get decent warranty support (pitted cone in front wheel). Incidentally, my recumbent dealer was absolutely super. Just the exact opposite.
I rode a 2003 OCR3 last year. Got it used, so I could convince myself that I'd be committed to riding. I think it's a good entry level bike. Not too heavy, fit was good for me (small), and for the most part the components were fine. The only issue for me was that as I got stronger as a rider, I began to push the bike more. The Sora components have a limit. I had trouble starting hard sprints and standing on climbs because sometimes the gears would slip. It did this even w/ a recent tune up. I've since sold the bike and upgraded it to an IF Planet X, but for the $330 I paid for used one, it was a great deal.
Fuji also do a good value entry level road bike.
If you are going to use this bike for winter riding or commuting, ensure that you can fit fenders and a lightweight luggage rack.
If you ever get a swish race bike, this will end up as your training machine for wet days.