Facebook seems to be have started out geared towards personal use but has morphed into a great tool for businesses as well. I have tried some of the advertising options for my business and I like that it gives you the ability to focus on a very specific area as well as specific age and income groups.
I find Twitter is easier to use because of the limits on content. It helps you to keep it short, sweet and to the point. I think its a great platform for business as well because its so easy to retweet and share relevant or interesting information.
I also use Instagram for my business occasionally but I am not proficient at all. I think this platform is great for businesses with artistic niches such as yoga so I hope to get better at it.
I am not familiar with Tumblr but my impression is that it is geared more for personal use and seems to be used by a younger age group. Pinterest seems to be geared toward niche markets such as fashion, photography and exercise so I think it would be a great tool for businesses like that.
With all these choices it's easy to get overwhelmed so I tend to stick with 2 or 3 platforms versus trying to maintain an online presence with all of them.