The best one will come down to personal preference. There are quite a number of tools available, and your use case might lean towards a subset of those at first glance.

It also depends on which platforms you'd like to interact with and what type of features you're looking for on each. If you're looking to schedule and post at certain times, it is a quite easy use case and you'll have plenty of choice.

The bottom line is, tools make your life easier. You can't imagine the content calendar of bigger brands and having to do everything manually. It's just not worth the effort at that point. At a smaller scale, you can take advantage of these tools to avoid repeated tasks, speed up your workflow and focus on what really matters.