Neither of these are that great. I can't say "相棒" really has the same connotation as "partner" does. It sounds more like something a girl would say when she doesn't want to commit to the relationship rather than a gender neutral alternative like it is in English.
this blog post does suggest it's closer to how "partner" is used in English so I should take back that the top one is inaccurate.
I am weary of accepting "based" translations just as much as "woke" ones, I think it's usually best to avoid any kind of baggage that might not exist in the other language.