I think its whoever the least shy and least awkward generally... though thats more of a suggestion than anything else.

I think culture has a lot to do with this, so as a disclaimer, I'm speaking as someone from the USA, so that's the standard I'm going on. Since we seem to have quite a few international users here now, which is all around great.

But anyway.
This is somewhat of an outdated...thing, I guess. Particularly in places where same-sex marriage is legal, it's kind of impossible to hold the whole the-man-proposes standard. What if there's not a man in the relationship? What if it's two men?

Not to mention our view of gender roles are different now, and women can be more outspoken and direct than they could in... say, the 1950's.

But this is an expectation that a lot of people seem to still have... that the man proposes. It's probably based around societal norms and such, but I know that if I had proposed to my fiance, a person assigned XY chromosomes, as a person assigned two X chromosomes, my extended family would have had a cow.

But anyway, moving on from my... whatever the last two paragraphs I typed are. Don't know what purpose they serve other than anecdotal...thing things. (It's like 3 AM I'm tired... forgive me. XD)

Anyway.
I think, if it's a surprise type proposal, whoever is actually asking to make the commitment should ask. Like whoever feels it's right.
But I know in my case, my engagement was something that was discussed the moment I got into my relationship with my significant other (which I also don't expect for most people, our relationship is somewhat a special case and we were pretty well commited before we got into the relationship, whether we knew it or not. It was pretty well inevitable, really.)

God, I sound like Excalibur. Or an old man. BAAACK IN MY DAAAAAAAY...

ANYWAY
ANYWAY
Man, I am an old man I lost track of whatever I was talking about....

ANYWAY.
Um
It depends on the couple and what they chose to do.
Yep.
Yep that;s my answer.
I'm very insightful, as you can see.
I'm very delighted to have brought you all to this delightful conclusion.

As They Said Above Me. It Doesn't Really Matter To Me !!!!

@8 I would say more but Im keeping my typing to a bit of a minimum right now so Ill just say.... A+ XD I agree with that 100%.

I wonder who picked "Men"? Anyway, it also doesn't bother me either. I was never the traditional type, nor do I plan to be.