Friendship, when it's the real deal, is love.
I went through a dark period when I did not have a romantic partner, my children had all moved away, and I had no friends because I'd just moved to another state. It was the loneliest, most desolate feeling I have ever had. My gal pals had been left behind. I missed them terribly, but they had busy lives, so I didn't get to see and talk to them as much as when we lived near each other.
As always before, I found it easier to establish fleeting relationships with men than to find real friendships in my new area. Those relationships couldn't replace the depth of intimacy I had with my gal pals, but my gal pals couldn't provide the same type of intimacy I had known with serious romantic loves.
For that reason, I treasure friendships as much as I do my committed relationships. Taking your question to the extreme, I'm asking myself, "Would I be torn between leaving my estate to my husband or my best friend?"
I'd have to say no, because of the frequency and regularity of how I interact with my spouse when compared to my friends and the social norms that don't expect such things of a friendship. Without a spouse or children, though, I wouldn't hesitate.