My bestfriend of my entire life so far was female, along with another. I have a past issue where I am a little wary of other males as friends. I'm completly heterosexual though, but most people think I'm not until they find out how much Hetero I can be. (Long funny story.).
Honestly, I think having a best friend as a guy would be really weird, and I'd be wondering if he was like one of my "previous" male best friends, who ended up being gay and... well, suffice to say, I haven't had a male best friend since I took him to court.
Once though, one of my female bestfriends ended up liking me, and I went along with it, developed an attachment to her, then when the relationship ended I lost her as a friend. (smack) I shouldn't have let things go so far, I looked up to her as a person.