Answering who is your best friend is a little like answering who is your favorite character in the Bible. The rules of theology (rightly) demand that we answer the latter question with the name that is above every name. And the rules of society today seem to demand that we answer the first question with: "my spouse is my best friend". To deny this is to perhaps cast aspersions on the quality of one's marriage.
Several years ago, if you asked me whether my wife is my best friend I would likely have been a little perplexed by the question. It seems weird to me, mainly because my wife belongs in a category that goes beyond friendship. How does a man compare his wife with several of his male friends, as if she is first but there is a second, or third best friend behind her? He doesn't. He shouldn't. We take away something from our marriages when we talk in this way, and we take away something from our friendships with people of the same sex when we speak like this.
For me, I'm content to say: she's my wife (and all that that ought to mean as far as the Scriptures are concerned; see Eph. 5:22-33).
As my Facebook friend, Peter Wallace, says: "It is only in the last generation or so that you will find people talking about their spouses as their 'best friends.' Until the late 20th century your best friends were all the same gender as you. I fear that the result of 'I married my best friend' is that most people do not have strong friendships outside of their marriage (which is disastrous for marriage -- since we need friends who know us well -- to help our marriage when we are in trouble). I wonder if anyone has studied the correlation between marrying your 'best friend' and divorce rates..."
Is Hallmark to blame? Is our increasingly effeminate culture to blame? I don't know, but I worry that men and women do not have strong friendships outside of their marriage, so their spouse wins by default. I don't want my wife to win because, well, I just don't have much to compare her with. I don't even want her in the "race", so to speak.
Regarding the "effeminate" culture, I think we are almost becoming afraid to say we have close male friendships because that could be construed too easily as "gay." Little wonder that pro-gay apologists have read this into the relationship between David and Jonathan. There is such a thing as a wife-centered home, whereby the wife is doted upon hand and foot, and where men simply don't spend enough time with other men. Likewise, there is a man-centered home where the husband gets to spend (a little too much) time with the boys, but the wife is constantly left watching the kids. Both are harmful situations.
In this world you are a blessed person if God gives you several friends, the type that stick closer than brothers (Prov. 18:24). Friends are gifts given by God to bless you, challenge you, support you, laugh with you, and counsel you. But they often do this in a very different way than your spouse. We're talking apples and oranges when we speak about how our spouses are friends to us and how others are friends to us.
When I think of spending time with my best friends a quote from C.S. Lewis comes to mind: "My happiest hours are spent with three or four old friends in old clothes tramping together and putting up in small pubs - or else sitting up till the small hours in someone's college room talking nonsense, poetry, theology, metaphysics over beer, tea, and pipes. There's no sound I like better than adult male laughter."
Or, similarly, Carl Trueman: "Drinking beer with friends is perhaps the most underestimated of all Reformation insights and essential to ongoing reform; and wasting time with a choice friend or two on a regular basis might be the best investment of time you ever make."
There's something else that strikes me as I think about this topic: when I'm around some of my closest friends, there is a sense in which my wife doesn't quite get how we talk and act the way we do. From her perspective, we're sometimes like immature kids, laughing our heads off about things she either doesn't understand or in which she fails to see the humor. Or she just isn't interested in some of the things we love. But, you see, that's the point: because of the radical differences between men and women, my wife isn't supposed to fully understand the nature and dynamic of my friendships with men. I only expect her to appreciate that they can give me something that she can't - and she can be content in that because God designed matters that way. I am more than happy to admit that her friends offer her something I can't.
We also need to consider the context in which this "my wife is my best friend" comment is made. Usually it is on Facebook for others to see. I tend to get a little worried when some people feel the need to tell the world constantly they have a good marriage. I don't go on Facebook and talk about how my best friends are my best friends. We simply live and act in a way that displays that reality. Likewise, with my wife, if I need to tell the watching world she is my best friend, then perhaps she should get worried. Or she will think I'm up to no good ("what do you want?" or "what have you done?").
As a close friend said to me recently, "It is even odd to say that your wife is your best female friend. She belongs to a category entirely her own. She is sui generis! We have various kinds of friends with women, but we only have sex with our wife. That is a deal changer. We are far more guarded with other women, and rightfully so. Thus, the husband-wife relationship cannot be compared to any other human relationship. 'An excellent wife who can find? She is far more precious than jewels.' To speak of your wife in categories that apply to other relationships is to denigrate both her and others."
Let's try to remember, the issue isn't about the phrase itself; the issue is about the underlying issues and the problems in our culture. Men and women need best friends of the same-sex. I find it a real pity when the spouse takes the place of those necessary relationships.
So if you ask me if my wife is my best friend, I would answer, "Of course not. She's my wife. Most of my best friends are balding."