I want a crusty bread from outside and super soft almost like a croissant inside. What flour should I use?
You need steam. For the first 10 to 15 minutes of the bake put a tray of water (about a cup full) in the bottom of the oven. Alternatively cover the loaf with some form of loose dome to trap in the moisture from the bread, again only 10 to 15 minutes then uncover.
Leave the steam for too long and the crust will get leathery.
I make Mark Bittman's no-knead bread. It is baked in a cast iron Dutch oven for the first 20 minutes of baking. Then, you uncover it for the last few minutes. This makes an excellent crust with tender, chewy bread inside. The other thing that makes a big difference with the crust is cooling the bread completely before slicing. It's hard to wait, but it's worth it.
You need AP flour for this. I know that most people in the English speaking countries will tell you to use "strong bread flour", but it produces an elastic crumb with some chewiness. For a really soft and fluffy inside, you need at least AP if not pastry flour.
As the others said, there are a ton of other things you need to produce this kind of bread, but you asked specifically about flour.
This is the most basic of breads. Use strong white flour, luke warm water (not milk avoid dairy which softens the crust) hydration of 65%, add 2% salt and 2% dried yeast (keep seperated) and about a 5% percent of lard cut into little chunks (not butter) for longevity. Lets assume you use 500g flour. That would be 325g water, 10g salt and 10g yeast + 25g lard. Put the whole mix except the water into a stand mixer and mix slowly until everything is incorporated. Add the water and mix until all is absorbed and the dough begins to loosen and become more liquid again. Now increase the speed to as fast as it will go and whizz for 4 minutes. It will come together. Scrape out with oiled hands and form a ball. Back into the mixing bowl which is also slightly oiled and cover with a shower cap or cling film and leave to rise until treble in size. Turn out onto a lightly floured board and knock back and shape or place in a tin folding edges underneath leaving a smooth top. Leave to rise again until treble in volume. Preheat oven to 220 degrees C. Make slashes in the top to encourage upward 'bloom', sprinkle with flour and bake for thirty minutes. Leave to cool uncovered - voila!!