I've tried several similar plug-ins, but wasn't satisfied until I found Shareaholic. This one has all the tools I was looking for, AND it looks the best! I love all the options for how to display the buttons, as well as the many options on where the buttons display. MUCH more flexible than any other similar plug-in!
The only thing I would change is for it to tell you who shared your posts. For example, if someone shares a Facebook post, it will tell you who and what caption they added, as long as their privacy settings allow it. I like to be able to see that so I can find out why people shared certain posts and give them more similar content.