Ramble Warning
TL:DR it depends on the song, post a link so I can listen to it.
Normally, I would do a combination of vocals and instrumental based on whichever is the most prominent. However, I would find myself favoring Vocals over the instrument.
So in sections with only instruments, I would map the most prominent one. But the moment vocals come in, instruments step aside (with exceptions of course).
I don't listen to hip-hop and this question depends on the song you're doing. So I am not sure, but here's one example I can give.
Example I Can Give:
One of the songs that I like is a cover of Drake's "God's Plan"
(https://www.youtube.com/watch?v=76mTtMCR4CU
)
Like at 1:29, you do a really cool switching between the beat and the vocals. This song is something I wish to map a later date...so don't steel it