Sami is such an awesome boys name, although I'm slightly biased because it's my brothers name! My dad is Arab and my mom is American, so it was a great arab-american name that they could both agree and compromise on.
My brother has never had any trouble with anyone mispronouncing his name. Sami is the more masculine spelling in my opinion, whereas Sammy seems more like a nickname for Samantha, and therefore more feminine.
Plus, I think all of his friends just call him Sam, and only family really calls him Sami.
I love it!