Indoor French Doors Vs the Others
The others will close off the space very effectively, but they do little to offer protection from sound. Small homes tend to be uncomfortable due to sound bouncing around everywhere, and the indoor French doors can offer more in the way of muffling some of that sound than the other types of dividers you can get.
Indoor French Doors are also great when you have stairs leading up to an apartment. You can use them to be sure you have all the privacy that you need in your apartment, and can even save a bit on your heating bills. If you have the indoor French doors at the top of the stairs separating your apartment from the stairs, you close that space off and you will feel more secure. You will not have to heat the stairs either, which can save you a lot of money. Because you usually only use the stairs to get in and out, heat is not really necessary.