Very often when this is asked, it's actually a linguistics question. It may be in disguise, to a greater or lesser extent, but it's usually a variant of
I'm using Google to obtain word/phrase frequency data, and those data are blatantly not consistent/reasonable. What the Heck?
As you can see from my answers, this is a linguistics question. Linguists such as M. Kilgariff have asked it, long since. And they have answered it too, generally to the effect that a Google Web Search "hit count" isn't the right tool for the job for a lot of reasons.
But it's also a fair bet that had that question been asked here it would have been objected to by people who entirely missed the "try and get a quick sense of which term is more widely used" in the question. This is someone who is doing a little bit of linguistic research on a couple of phrases, and wondering why the tool that xe is using is providing nonsense answers, and whether it's even the right tool to be using. But it's possible to miss that and mis-read this as a question about how Google works rather than as a question about whether Google can be used as a tool for linguistic analysis.
So how would you have phrased this question for this readership of "professional linguists"? Would you have seen it as a linguistics question as it stands?