Two seat sofas generally have wider (more comfortable?) cushions. Also, even if you have a 3 cushion sofa you'll rarely see more than 2 people sitting on it at a time. It's just too cramped for 3 people.
Despite all of that, there are far more 3 cushion sofas sold than 2 cushion sofas. So, have fun making your decision.
Two cushions can often be more contemporary than three cushions but not always.
Cochrane is an old line furniture company that has been around for over a hundred years. They are primarily known for their solid maple dining rooms but also make high quality bedrooms and living room furniture.

I prefer a 3 cushion couch. If you do have 3 people sitting on the sofa at one time, the center person does not end up sitting on the crack between the cushions.

I think it's true that a 3 cushion sofa is more practical and common than the 2 cushion loveseat. I say this even though I think that usually you'll only have 2 people sitting on it at a time-- unless you have 3 very close family members coming over. It's cultural I think. We Americans like our distance. I got to a lot of discount furniture places and the loveseats far outnumber the sofas.

I have a two cushion in the living room and a three cushion in the den. I much prefer the three cushion for comfort and so that three people can be comfortable.

If your sofa will be used by three people from time to time, I highly recommend three cushions over two. The three cushion works well in all situations. If I take a nap on it, my hips don't end up in between the cushions (not that they fit!).

Here's my experience -

People would rather sit on the floor than be the third person on a couch.

Now that our kids are grown, we really crowd the house at the holidays. We host the holiday meal, relatives are included and the kids' spouses and SOs. Therefore, a 3 cushion sofa is the answer for us at this point in our lives.

Here's my 2 cents worth here. I have both. On the two cushion couch the center (where to two cusions meet)tends to push up in the center because the majority of the use is on the edges. The 3 cushion don't do that. When I do it over, I would prefer two love seats over a couch and love seat.

I am purchasing an 8 foot sofa from Restoration Hardware....two cushions or three?