Is there a single English word equivalent that means 人各有志? I think I could say something like "differing opinions/perspectives/thoughts/etc." I'm wondering if I could somehow say this with one word?
I can't think of a single word.

The phrase for the meaning you're describing is De gustibus non est disputandum, or sometimes colloquially "to each his own".

This is not however the literal meaning of 人各有志. The most analogical word is aspiration in English; e.g. "each man has his own aspiration".