Hey! So if you just need it for purely scheduling, Buffer is no-fuss and I would 100% recommend them. BUT if you want to manage comments/engagements, have in-depth reporting and analytics, I would recommend Sprout Social.
I haven't tried Hubspot before, but I've used Sendible and Planable. If you need clients or a "higher up" to approve posts, Planable can do it, but they can't auto post to IG (you have to schedule it, then the phone app notifies you) which is one of the main blockers.
If Sprout Social is out of your budget, I recommend checking out Social Report! It's what I use when I need complete management but I use Buffer for when I need just scheduling.
Hope this helps, LMK if you have questions.