The best thing is to do as your recipe directs it, because there are several considerations that play together here.
First, if you have a very exact recipe where you measure each ingredient and mix together in a mixer, it doesn't matter that much. Just dump it in the mixer and turn on, making sure to scrape or rest as needed until the texture is right.
If you again have an exact recipe but are mixing by hand, I suggest that you do it flour-first, because that reduces lumps.
If you have a recipe where you are starting with one ingredient and are going to add more of the other until the desired consistency is reached, the main constraint is the yeast. If you are starting with the yeast in the flour (as is typical with dry yeast), then you should always start with the measured flour+yeast mixture and add water until ready. If your recipe has you start with the yeast in the water (needed for cake yeast, but some converted recipes also suggest it for dry types of yeast) then you should be adding flour to the water and not the other way round. Here, you can avoid the lumps problem by not dumping flour on top of the water, but using the volcano method where you add the water to a depression in a flour heap and slowly mix in more flour from the crater walls until you have it the way you want it. The volcano method works better on flat surfaces rather than bowls, you can use a baking sheet or a big baking tin to gain some control of the mess.