Just picked up(and am posting from) the G74sx after wrestling with this very question, here are some of the things that went into my decision. The GPU was a major deciding factor because it is one area that cannot be conveniently upgraded to extend the life/power of the machine. For this reason I went with one of the stripped down versions, no BlueRay, only one 500mb HD, etc. but avoided the BBK7 because it has the neutered GPU and Display.
As far as the keyboard goes, I updated the ATK/BIOS right off so I can't speak to any errors with the default system. From what I have seen, this has fixed almost any keyboard issue posted, at least for those who reported their results after having tried it. Since then the only issue I've encountered has to do with my lack of accuracy while getting accustomed to a new keyboard style.
On the audio side, adjusting the THX TruStudio every reboot is mildly annoying, but that is a short term software issue and thus wasn't a factor for the decision. There is a noticeable, if slight, lack of base, but the overall speaker sound quality is quite acceptable. I use earbuds or a gaming headset most of the time so my experience in this area is not terribly extensive and YMMV.
Great experience so far, though I still have a ways to go in order to put this through its paces for gaming performance. The most pleasant surprise was the lack of bloatware to uninstall, I was all set to do a clean wipe but it really does not seem necessary.
That was a bit more long-winded than anticipated, but I hope some of it has helped.
edit:To answer your question directly, the 73sw has been out long enough to work out the kinks and is likely the more stable at the moment. However the minor nature of issues with the 74sx and the rate that past ones have been fixed makes it the better choice in my eyes.
