top bud

One's closest or favourite friend; a person's best friend.

I got out my bed at 2 in the morning to go and pick my top bud up from town. That's what besties are for.

Topbud

It's a person who knows that you are completely insane, but loves you anyway. Best friend material.

I just got back from Paul's funeral. His topbud made a very humorous elegy about all the crazy things they did together in their youth.