I have yet to find a social sharing plugin that's truly lightweight and has no bugs.
I was using GetSocial, but though it's lightweight it seems quite buggy - for instance on some of my sites, if I select not to show it on the home page, it works. On others, it doesn't. The Pinterest button shows on some but not on others. And so on.
So I'm back to Sexy Bookmarks but it does slow my site down a bit. What else is good?