We (me and my wife) bought a (2 bed) semi-detached Bungalow as our first property together. Where we live the ftb options are terrace with no garden or driveway, or a bungalow with garden and a driveway, so for us it was an obvious choice. It worked very nicely for the two of us, but as soon as we had my daughter we realised it was a bit small! Having the central corridor makes it hard to move about quietly without waking everyone. I get up for work about 5am so it's hard to get ready quietly when you are right next to everyone. Now we have moved to something with an upstairs, it't nice to be able to put my daughter to bed upstairs and still do things downstairs without disturbing her. I can also have breakfast downstairs without waking anyone. This is nothing to do with having anymore space, it's just nice to have the two floors! Though having said that, the increased space is handy for toys etc as we are not constantly surrounded by them! The lack of stairs in the bungalow also don't mean no stairgate, as we had one on the kitchen doorway in the bungalow to separate it from the rest of the house.
Dave