There's a number of choices. Buffer.com and Hootsuite.com are amongst the most popular and both have free and paid options as well as apps for your phone and tablet.
I don't think Buffer does Instagram yet and I think it's only on the paid versions of Hootsuite - I'm not sure though on that, it was at one point at least.
As i have used free plans of both buffer and Hootsuite, i can say that buffer doesn't offer Instagram post scheduling, but hootsuite does. So my vote goes to Hootsuite.
Just as an aside, the Chrome extensions for both Buffer and Hootsuite are really good too. If you're on a page you want to share, a simple right click of the mouse and you can share it to whichever networks you want and comment on it.
I use Tweetdeck, it is completely free (owned by Twitter) and can schedule tweets and allow you to view multiple feeds. I have never tried Hootsuite so can't comment but I believe that to be very popular too. Buffer is a very good tool to publish content through multiple social networks thus saving you time.
I have also used Tweetdeck and I think it's quite useful to sort your newsfeed and skip the stuff you don't need. I have also used IFTTT which is really great and gives you an opportunity to connect a few social profiles. It could be set, for example, if you post something on facebook to post it automatically to Twiter. Or if you save a pin, to post it right away on facebook and a lot of different options such as
- Mute your phone when you arrive at work
- Save your new Instagram photos to Dropbox
- Share your Instagrams to Facebook
- Save all your Gmail Attachments to Dropbox
and much more
Lastly, I used it a couple of months ago and it was free.
Hootsuite is really good once you get organised with your streams and teams. Will post to Instagram but not directly. It sends a notification to your phone for you to activate.
Hootsuite will also post to Pinterest using the app Tailwind.