I've used Schedugram, Hootsuite, and Buffer. My favorite (hands down) is Schedugram. It's so easy to bulk upload photos, edit captions, and schedule posting. It's also easy to bounce between multiple accounts (as an agency we have a lot of different accounts) AND you can see your scheduled posts on a calendar view, which somehow makes it easy for me to understand.

You can't schedule the first comment on the post, which stinks if you want to add hashtags to the post instead of the caption.

I love that I can add location, tags, and even a first comment (hello, hashtags!)

There have been a few times where for some reason, my posts failed to publish. Also, I wish there was an option for Instagram stories.