Seems like a lot of MTB guys around here are interested in a cyclocross type bike, myself included. I've recently been doing some research into the different groupsets and have decided to most likely go with SRAM rather than Shimano or Campagnolo.
Word seems to be that the Shimano hydraulic brakes (which I've also researched and also sided in favor of) reign as the best much like they do in the MTB world. I was told the SRAM brakes had issues and had a recalls not long ago.. not sure if that's still a concern, but the consensus still seems to be that the Shimano brakes are better. The Shimano groupset also has a rep for being pretty durable whereas the SRAM has the opposite rep with complaints of shifters breaking, internal ratchets failing, etc).
I know.. why in the heck would I choose SRAM then?
On the flip side, the SRAM "crispness" in shifting is preferred by lots of people. Many complain that Shimano is too "light" so to speak, and I understand what they mean from having experience with the same things on my MTBs, of course. The other downside for the Shimano that is pushing me towards SRAM is that Shimano seems to be the most susceptible to getting contaminated from environmental conditions - Which is even more of a concern with a CX bike.
So, to summarize, this is why I've chosen SRAM for a CX build:
-Assuming they have their brake issues sorted (seems to be the case but not sure)
-Crisper shifting
-More reliable drivetrain performance when it gets dirty/muddy
-Even though durability seems questionable, all parts are easily rebuildable and SRAM has a quality warranty service.
All in all, if I built a CX bike I'd go SRAM Apex for a good value, well performing groupset. If I build a road bike I'd go Shimano. The lighter shifting fits better on the smooth road and the issues with performance when it's gets contaminated is not a concern on the road usually. Thing is, if I built a road bike I probably won't be doing a budget build like if I do a CX build; I'd want mechanical shifting and all the other high end components that would do justice to such a cool technology.
Also, I'd most likely do all chiner handle bar, stem, post etc as I'm not concerned at all with failures and I don't want to spend more than I have to. Others may want the "mental security" of some higher end, name brand stem/post/bar though, so to each his own.
Hope that helps. Link to some of the Giant bikes you're considering, I'd be interested to see what you have in mind.