Well it highly depends on what you want to achieve. Facebook is pretty great for every niche as much as I know, but it's very strict and you need a lot of time, patience and knowledge to be successful with it.
IG on the other hand is not as strict as Facebook. Great for CPA, Freebies and E-Commerce. Pinterest works for some niches much better than others. DIY, health, fitness, travel, blogging, parenting, books, makeup,.... works very good with Pinterest.
I mostly use social networks to market B2B products. Top 5 most useful social networks for me have been:
1. Facebook (posting to niche groups can drive a lot of traffic, i love the fact that facebook has bigger account limits - you can join more groups, no limit on content like twitter)
2. LinkedIn (same as facebook, posting to niche groups can drive a lot of traffic, but group moderators can be unfair sometimes)
3. G+ (posting to the right groups can drive lots of traffic)
4. Pinterest - Haven't used it myself but my site visitors share posts to pinterest, which in turn drives traffic
5. Reddit - posting interesting non-promotional content to right subreddits can drive quality traffic
Facebook has to be first, as it actually pushes promotion and has access to the largest possible userbase. Right after it I'd go with Twitter (also inclined to promotion), Instagram (best website to cater to a younger audience), Pinterest and Reddit. To me, Google+ doesn't do much that the others can't, and Tumblr isn't promotion-centered enough to justify its usage.