I just realized that some people object to hedonistic utilitarianism (which I've traditionally favored) on the grounds that "pleasure" and "suffering" are meaningless and ill-defined concepts, whereas I tend to find preference utilitarianism absurd on the grounds that "preference" is a meaningless and ill-defined concept.

This seems to point to a difference in how people's motivational systems appear from the inside: maybe for some, "pleasure" is an obvious, atomic concept which they can constantly observe as driving their behavior, whereas others perceive their own actions as being driven more by something like a "preference" that seems like a coherent and obvious concept to them, and others still don't feel that either of these concepts is particularly central, causing them to disregard utilitarianism. (Of course one may also reject utilitarianism for other reasons.)