I guess it's good to have both, since the who have their own ups and downs.
Having a boy best friend feels good. Yes, there's a chance you might fall for each other and risk ruining your friendship, but if you always feel that way, then you might miss out on having a hell of a greeeat best friend. I mean, you can choose not to fall for him, and chances are you two don't fall for each other, OR if you do, and you two are lucky, you both feel the same, then yey. PERFECT COUPLE. HAHA. Enough about it, it's nice to have a boy best friend because there is NO DRAMA at all. Well except for the falling in love with each other part, but aside from that NO DRAMA AT ALL. You get instant un-biased advice from a guy's perspective. You got your own body guard to malls, parties, etc. And you got back up when a certain someone breaks your heart.
Having a girl best friend on the other hand, has its perks. Shopping buddies, confidante, sister, mother and so on and so forth. There are some stuff that you can't tell a guy, stuff that only GIRLS can understand. But you also risk drama, falling for the same guy, jealousy and the other likes.
So yes, there will always be downs in friendships. And what's important is you take that chance, that risk to see if its all worth it. Because most of the time, they are.