should client advertisement banners be do-follow or no-follow

so a i have a few clients that reached out to me and would like me to place advertisement banners + link to their sites

i'm using standard html to insert them

example:

<a href="https://xxx/.com"><img src="https://xxx.png" /></a>

what's the best practice for this, should i insert them as do follow or no follow?

I would choose nofollow, better safe than sorry, plus no point to leak out your seo juice

Also I would better add to your link target="_blank" for not loosing your users.