My sister is one of my best friends. I couldn't nor wouldn't want to make it through my days without her as she is (1) so much fun, and (2) is an amazing support system. I met the girl when I was just 3 years old and while she used to annoy me, a lot, we are now closer than ever.
Now that's not to say we haven't had our fair share of disagreements; her copy-cat tendencies, my dependency on her to play with me (that's what sisters are for, right?), and everyone being convinced that she was the perfect child (I mean, she did used ask if she could go to bed when she was tired... who does that? Don't even get me started on that fact that she used to 'tell' on herself when she did something bad)... and I was not.
However, there have been many great things about being sisters; me knowing exactly how she's feeling and being able to speak for her for several years when we were younger, 'No, she doesn't need to go to the bathroom, Mom', having someone to dress up in ridiculous costumes with on random days, and of course, in the later years, party with, laugh with, and share secrets with.
Sister, you're amazing and I love you and I'm so lucky to have the best sister in the world that is you.