Frequently commenter miko offered this up for consideration:
Being only ever first (or last) might make you look independent but also might make you look uncollaborative or, more likely, that no one likes you.
Fascinating remark. Have you ever heard anyone say this for real? Not in terms of mere publication numbers, I've heard that one more than once (as in "Can't you just get on some more papers" from people concerned about a thin publication record from an earlier-career scientist). But in terms of your ability to collaborate productively. Play well with others, so to speak.
I can't really remember hearing this. Mostly people are only mentioning collaborative, middle-author contributions to denigrate the person's level of independence and/or to try to subtract credit from their publication count.