I use two social media platforms in a big way - Twitter and Instagram. I've never been a major fan of Facebook but have set up a Pigsy page on there.
Twitter and Instagram appeal to me for two very different reasons. I like the visuals of Instagram and I like the short and sweet nature of twitter and the fact that you have to limit your tweet to 140 characters. I also think that Twitter has been very much improved since you can add images to it.