Yes, you do need to be careful on this one. For example, as UK citizen entering the US on the VWP, you are restricted as to what kind of work you can do. Answering "business" will inevitably (IME) end up with a series of follow-up questions to determine what kind of thing you'll be doing.

I've had some bizarre exchanges, usually in ORD, where I've been unable to figure out whether it's a tactic to ensure I'm being consistent, or just an officer being weird. Lines like "I can't understand how you can do your job, if you're out of your office most of the time" (I was a consultant at the time). Mind you, I had committed one of the biggest sins on that occasion: not remembering the dates I'd last been in the US (I was going to the US a couple of times a year at that point, but travelling internationally every couple of weeks. Sorry, America, you're not so special that I have the dates I visited inscribed upon my memory - although I do look it up when I'm on the plane these days).

(Another odd exchange was at JFK, where, on saying we were here visiting friends and on holiday, the immigration officer went off into an unprovoked, bizarre rant about how busy the place was because so many people, from all over the world, were so desperate to come to New York. Much as I think NY is a wonderful city, and much as I appreciate the "bring us your poor, your tired, your tired, your huddled masses yearning to be free" ethos, I did have to bite my tongue to avoid pointing out that he wasn't helping how busy it was by wasting several minutes with his rant, and that we'd just arrived from LHR, an airport that handles 30% more passengers than JFK. But, you know, it's nice that he's proud of his job, we could all do with more of that...)

So I tend to answer "holiday/vacation" [depending on country], "business meetings" or "in transit to [x] [with/without a stopover]". It seems to go more smoothly that way.