I read the high level details on CC-GNU GPL 2.0, and Creative Commons used by SO. I'm not a lawyer, so I'm not sure I get the specific pros and cons of each variation of open source license.
What is the difference between the popular GPL's and Creative Commons' licenses in terms of what a software developer or company has to gain or lose by choosing particular terms when releasing an open source project?
Aside from the technical details and incompatibilities, Creative Commons licenses aren't meant for software or software documentation. Check the Creative Commons FAQ and what FSF says about it.
Creative Commons is created for all types of content, GPL is designed in particular for Software. So the main difference is, that the CC-license don't demand, that you have to release the 'source'. For simple texts (like in stackoverflow) or music, there may be no source-form.
Other differences are, that CC is a system of licenses, different restriction can be combined. Stackoverflow uses Creative Commons Share-alike, the Share-alike-restriction is similar to GPL, in the way that every derived work has to be licensed in the same way. Other possible restriction for CC-licenses are non-commercial and non-derivate.
And the CC-licenses have a simple text, that is easy to understand, not only the difficult lawyer-stuff.
There are different types of Creative Commons licenses. The ones that are considered "free" (by the Free Software Foundation) are the Attribution (by) and the Attribution Share Alike (by-sa), the former being a non copyleft license.
If a license isn't copyleft, it allow others to distribute your work under a different license than the one you used (this is something you probably want to avoid). So I would discard the Attribution (by) license.
On the other hand, the problem with all the CC licenses is that they aren't designed for software, so they don't take into account concept like source code, or linking from code with a different license (specially important if you're developing a library, for example). Both the GPL and the LGPL makes you distribute the source code with any modification you make (only if that modification is distributed, off course). The difference between them is whether you allow people to link to your code from code using a different license. The LGPL license was designed to allow this.
I would use the GPL, but you should think carefully before releasing software under a free license (although I'm totally in favor of this), because ones it's done, you can't go back. I've heard a few stories of companies trying to do this (don't remember exactly their names) and it didn't go well for them.
The only thing I have to add is that the standard IANAL caveat also applies. Get an attorney to review the issue if you're not sure about questions like these: they'll be the only ones who can tell you for sure.
Other than that, if you're looking for alternatives to the GPL, my suggestion is to look at the OSI's list of open source licenses. I don't necessarily recommend all of those though. My advice is to stick to the "Licenses that are popular and widely used or with strong communities" heading unless you have a really good reason not to.