Almost Couple vs. Couple--Which One is More Interesting to Read?

So I was having a discussion this morning about what is more interesting to read in a romantic suspense book---a couple that is working their way toward each other during dangerous circumstances and having those first stirrings of attraction/love, or a couple that is already together.

At first my response was, it depends on the story and how well-written it is, because if the plot is stupid, it doesn't matter about the couple.  But then I thought a little more about it.

There are movies like Mr. and Mrs. Smith about a married couple in the spy business, but I don't think those are the norm for a reason.  As many TV writers tell you, it is hard to write material for a couple when they're already together.  The tension leading up to a couple getting together is what sells it.  (I'm reminded of one of my favorite spy shows, Alias, and one of the things that totally sold that show was the relationship with Sydney and Vaughn.  I loved them).  I think the same may be true in books.  Who didn't love the relationship between Mr. Darcy and Elizabeth?  *le sigh*

But if we go back to TV shows for a minute, in my favorite show, Castle, (only a month until the season premiere.  Eeee!) many people have been clamoring for Kate and Rick to get together for at least two years.  The writers have thrown obstacles in their path, some of them stupid, but regardless, it's taken four seasons for them to get close to taking their relationship to the next level.  Writer/producers/fans have all gone back and forth and it came down to, "we don't want the Moonlighting curse."  Meaning, of course, that old show Moonlighting with Cybill Shepherd and Bruce Willis which is "proof" that supposedly once a couple is together it kills the show.  (Although I think there were extenuating circumstances beyond the getting together on Moonlighting, but that's another story.)  Then the creator of Castle came out and said that he feels there's a lot of intricate stories you can tell once a couple is together. Yay!  I think so, too, but it takes more creativity and work, I think.  I hope he makes that come true for Castle this season.

Anyway, I digress.  For me, in my favorite books I love the tension with the couple, the dance and the romance while skirting terrible danger.  In my own books, I always write the couple as getting to know each other and falling in love under stressful circumstances.  In the project I'm mapping out now, though, it's the sequel to Ribbon of Darkness, and Kennedy and Ethan are already together.  This is a new experience for me and I'm wondering if I can do it justice just because dynamics are different when you have a couple that is already together vs. one that is just getting together.  It's fun and exciting and scary, too.

What do you think?  Do you find almost-couples or already couples more interesting to read about?  Who are your favorite fictional couples?