Answer: All of them.
If the variety of shapes seems puzzling, consider this: all baguettes are French bread, but not all French breads are baguettes.
As dictated by French law, real French bread contains flour, water, salt, and yeast. The real deal contains no fats, no sugar, and no preservatives, which is why French bread should be eaten the day that it is made. Leftovers are best when transformed into French toast or ground into breadcrumbs.
Still wondering about the shapes?
The same basic dough was used to make all of these loaves. Forming them into different sizes and shapes is not a baker's marketing ploy. Baking loaves with different lengths, widths, and thicknesses produces differences in texture.
The long, thin baguette on the far left has more crust and less interior than the shorter baguette next to it. Both will be delicious, but the long thin one will be slightly chewier and denser.
Different shapes lend themselves to different applications. The demi-baguette (third from the left) is a great size for a hearty sandwich while the rounded Boule is perfect for thick slices of toast.
The top, horizontal loaf is the shape that most Americans identify with "French bread" when not meaning "baguette." This large, wide loaf has a high ratio of interior to crust -- perfect for making a savory Croque Monsieur.
Insider tip: Some companies make this big, friendly loaf with hidden fats and preservatives. Do yourself a favor and check the ingredient list before buying.
From bakery to bakery (especially in grocery stores), you will find a lot of variation in the names applied to identical loaves of bread. For instance, the long thin loaf might be tagged baguette, Ficelle, Baton, French Stick or just plain old French bread. Don't let that throw you.
If you are buying bread for a recipe, look for descriptive terms in the recipe to guide you. For example, "baguette"
If you are buying French bread to accompany a meal, the most important factors are good ingredients and freshness. After that it's simply personal taste.
The only thing you must never do when buying French bread is worry too much about it. Fresh bread, no matter what variety, is one of life's true pleasures and adds a special touch to any meal.